fix: vim.eval should treat Vim boolean as Python bool #603

Problem:
- In Nvim, Vim bool is evaled to string, but in Vim 8+, it is evaled to
  Python bool. So pynvim's legacy vim.eval is not compatible with Vim
  8+.
- Previously, the argument against compatibility with Vim 8+ in this
  aspect is that adding checking for Python bool would be slower. But if
  we use `type(obj)` with operator `is`, it would be 3% ~ 80% faster
  than the current num_to_str implementation (more complex obj seems to
  have more performance gain).

This is the script I use to benchmark
```python
import timeit

num_types = (int, float)

def num_to_str(obj):
    if isinstance(obj, num_types):
        return str(obj)
    else:
        return obj

def num_to_str2(obj):
    obj_type = type(obj)
    if obj_type is int or obj_type is float:
        return str(obj)
    else:
        return obj

def num_to_str3(obj):
    obj_type = type(obj)
    if obj_type == int or obj_type == float:
        return str(obj)
    else:
        return

test_cases = [
    (100, "Integer"),
    (10.5, "Float"),
    (True, "Boolean"),
    ("hello", "String"),
    ([1, 2], "List"),
    ({'a': 1, 'b': 2}, "Dict"),  # Restored!
]

def run_benchmark():
    # Using a fixed format string for perfect alignment
    fmt = "{:<15} | {:<10} | {:<18} | {:<18} | {:>9}"
    header = fmt.format("Input", "Type", "isinstance (s)",
                        "type is (s)", "type == (s)")

    print("\n" + header)
    print("-" * len(header))

    for val, label in test_cases:
        setup = "from __main__ import num_to_str, num_to_str2, num_types"

        # Number of loops: 1,000,000
        t1 = timeit.timeit("num_to_str(obj)", setup=setup,
                           number=1_000_000, globals={'obj': val, **globals()})
        t2 = timeit.timeit("num_to_str2(obj)", setup=setup,
                           number=1_000_000, globals={'obj': val, **globals()})
        t3 = timeit.timeit("num_to_str3(obj)", setup=setup,
                           number=1_000_000, globals={'obj': val, **globals()})

        display_val = str(val)
        if len(display_val) > 14:
            display_val = display_val[:11] + "..."

        print(fmt.format(display_val, label, f"{t1:.4f}",
                         f"{t2:.4f}", f"{t3:.4f}"))

if __name__ == "__main__":
    run_benchmark()
```

And the benchmark result:

```
Input           | Type       | isinstance (s)     | type is (s)        | type == (s)
------------------------------------------------------------------------------------
100             | Integer    | 0.1125             | 0.1095             |    0.1118
10.5            | Float      | 0.3256             | 0.2512             |    0.2791
True            | Boolean    | 0.0731             | 0.0604             |    0.0788
hello           | String     | 0.1005             | 0.0600             |    0.0793
[1, 2]          | List       | 0.0940             | 0.0602             |    0.0755
{'a': 1, 'b...  | Dict       | 0.1080             | 0.0599             |    0.0759
```

So clearly using `type(obj)` with `is` is the fastest way.

Solution:
- Use type(obj) with is operator is to check for exact number

Author: brianhuster

README.md

@@ -63,9 +63,6 @@ Pynvim defines some extensions over the vim python API:
 
 See the [Python Plugin API](http://pynvim.readthedocs.io/en/latest/usage/python-plugin-api.html) documentation for usage of this new functionality.
 
-### Known Issues
-- Vim evaluates `'v:<bool>'` to `<class 'bool'>`, whereas neovim evaluates to `<class 'str'>`. This is expected behaviour due to the way booleans are implemented in python as explained [here](https://github.com/neovim/pynvim/issues/523#issuecomment-1495502011).
-
 Development
 -----------
 

pynvim/plugin/script_host.py

@@ -195,7 +195,8 @@ def writelines(self, seq):
 
 
 def num_to_str(obj):
-    if isinstance(obj, num_types):
+    obj_type = type(obj)
+    if obj_type is int or obj_type is float:
         return str(obj)
     else:
         return obj