[ty] Include synthesized arguments in displayed counts for too-many-positional-arguments (#18098)

## Summary

Resolves [#290](astral-sh/ty#290).

All arguments, synthesized or not, are now accounted for in
`too-many-positional-arguments`'s error message.

For example, consider this example:

```python
class C:
	def foo(self): ...

C().foo(1)  # !!!
```

Previously, ty would say:

> Too many positional arguments to bound method foo: expected 0, got 1

After this change, it will say:

> Too many positional arguments to bound method foo: expected 1, got 2

This is what Python itself does too:

```text
Traceback (most recent call last):
  File "<python-input-0>", line 3, in <module>
    C().foo()
    ~~~~~~~^^
TypeError: C.foo() takes 0 positional arguments but 1 was given
```

## Test Plan

Markdown tests.

Author: InSyncWithFoo

crates/ty_python_semantic/resources/mdtest/call/constructor.md

@@ -47,7 +47,7 @@ class Foo: ...
 
 reveal_type(Foo())  # revealed: Foo
 
-# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 0, got 1"
+# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
 reveal_type(Foo(1))  # revealed: Foo
 ```
 
@@ -62,7 +62,7 @@ reveal_type(Foo(1))  # revealed: Foo
 
 # error: [missing-argument] "No argument provided for required parameter `x` of function `__new__`"
 reveal_type(Foo())  # revealed: Foo
-# error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 1, got 2"
+# error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 2, got 3"
 reveal_type(Foo(1, 2))  # revealed: Foo
 ```
 
@@ -84,7 +84,7 @@ reveal_type(Foo(1))  # revealed: Foo
 
 # error: [missing-argument] "No argument provided for required parameter `x` of function `__new__`"
 reveal_type(Foo())  # revealed: Foo
-# error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 1, got 2"
+# error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 2, got 3"
 reveal_type(Foo(1, 2))  # revealed: Foo
 ```
 
@@ -105,7 +105,7 @@ def _(flag: bool) -> None:
     # error: [missing-argument] "No argument provided for required parameter `x` of function `__new__`"
     # error: [missing-argument] "No argument provided for required parameter `x` of function `__new__`"
     reveal_type(Foo())  # revealed: Foo
-    # error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 1, got 2"
+    # error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 2, got 3"
     reveal_type(Foo(1, 2))  # revealed: Foo
 ```
 
@@ -198,7 +198,7 @@ reveal_type(Foo(1))  # revealed: Foo
 
 # error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
 reveal_type(Foo())  # revealed: Foo
-# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
+# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 2, got 3"
 reveal_type(Foo(1, 2))  # revealed: Foo
 ```
 
@@ -217,7 +217,7 @@ reveal_type(Foo(1))  # revealed: Foo
 
 # error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
 reveal_type(Foo())  # revealed: Foo
-# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
+# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 2, got 3"
 reveal_type(Foo(1, 2))  # revealed: Foo
 ```
 
@@ -238,7 +238,7 @@ def _(flag: bool) -> None:
     # error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
     # error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
     reveal_type(Foo())  # revealed: Foo
-    # error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
+    # error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 2, got 3"
     reveal_type(Foo(1, 2))  # revealed: Foo
 ```
 
@@ -344,7 +344,7 @@ class Foo:
 reveal_type(Foo())  # revealed: Foo
 reveal_type(Foo(1))  # revealed: Foo
 
-# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
+# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 2, got 3"
 reveal_type(Foo(1, 2))  # revealed: Foo
 ```
 
@@ -363,7 +363,7 @@ class Foo:
 # error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
 reveal_type(Foo())  # revealed: Foo
 
-# error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 0, got 1"
+# error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 1, got 2"
 reveal_type(Foo(42))  # revealed: Foo
 
 class Foo2:
@@ -376,7 +376,7 @@ class Foo2:
 # error: [missing-argument] "No argument provided for required parameter `x` of function `__new__`"
 reveal_type(Foo2())  # revealed: Foo2
 
-# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 0, got 1"
+# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
 reveal_type(Foo2(42))  # revealed: Foo2
 
 class Foo3(metaclass=abc.ABCMeta):
@@ -389,7 +389,7 @@ class Foo3(metaclass=abc.ABCMeta):
 # error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
 reveal_type(Foo3())  # revealed: Foo3
 
-# error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 0, got 1"
+# error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 1, got 2"
 reveal_type(Foo3(42))  # revealed: Foo3
 
 class Foo4(metaclass=abc.ABCMeta):
@@ -402,7 +402,7 @@ class Foo4(metaclass=abc.ABCMeta):
 # error: [missing-argument] "No argument provided for required parameter `x` of function `__new__`"
 reveal_type(Foo4())  # revealed: Foo4
 
-# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 0, got 1"
+# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
 reveal_type(Foo4(42))  # revealed: Foo4
 ```
 

crates/ty_python_semantic/resources/mdtest/call/subclass_of.md

@@ -24,7 +24,7 @@ def _(subclass_of_c: type[C]):
     reveal_type(subclass_of_c("a"))  # revealed: C
     # error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
     reveal_type(subclass_of_c())  # revealed: C
-    # error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
+    # error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 2, got 3"
     reveal_type(subclass_of_c(1, 2))  # revealed: C
 ```
 

crates/ty_python_semantic/src/types/call/bind.rs

@@ -1285,14 +1285,8 @@ impl<'db> Binding<'db> {
                     first_excess_argument_index,
                     num_synthetic_args,
                 ),
-                expected_positional_count: parameters
-                    .positional()
-                    .count()
-                    // using saturating_sub to avoid negative values due to invalid syntax in source code
-                    .saturating_sub(num_synthetic_args),
-                provided_positional_count: next_positional
-                    // using saturating_sub to avoid negative values due to invalid syntax in source code
-                    .saturating_sub(num_synthetic_args),
+                expected_positional_count: parameters.positional().count(),
+                provided_positional_count: next_positional,
             });
         }
         let mut missing = vec![];