Update type annotations for passes (#2230)

More clear on the documentation site.

Author: justinchuby

onnxscript/ir/passes/_pass_infra.py

@@ -16,7 +16,7 @@
 
 import dataclasses
 import logging
-from typing import Sequence
+from typing import Literal, Sequence, final
 
 __all__ = [
     "PassBase",
@@ -180,23 +180,31 @@ class InPlacePass(PassBase):
     """A pass that modifies the input model in place and returns it."""
 
     @property
-    def in_place(self) -> bool:
+    @final
+    def in_place(self) -> Literal[True]:
+        """An in-place pass is in place."""
         return True
 
     @property
-    def changes_input(self) -> bool:
+    @final
+    def changes_input(self) -> Literal[True]:
+        """An in-place pass changes the input model."""
         return True
 
 
 class FunctionalPass(PassBase):
     """A pass that returns a new model but does not modify the input model."""
 
     @property
-    def in_place(self) -> bool:
+    @final
+    def in_place(self) -> Literal[False]:
+        """A functional pass is not in place."""
         return False
 
     @property
-    def changes_input(self) -> bool:
+    @final
+    def changes_input(self) -> Literal[False]:
+        """A functional pass does not change the input model."""
         return False