fix: use plain type: ignore for cross-version mypy compatibility

Different Python/mypy versions report different error codes for the
same type issues (return-value vs no-any-return). Using plain
`# type: ignore` comments avoids unused-ignore errors across versions.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: bokelley

src/adcp/types/coercion.py

@@ -62,8 +62,8 @@ def validator(value: Any) -> T | None:
                 return enum_class(value)
             except ValueError:
                 # Let Pydantic handle the validation error
-                return value  # type: ignore[return-value]
-        return value  # type: ignore[return-value]
+                return value  # type: ignore
+        return value  # type: ignore
 
     return validator
 
@@ -82,7 +82,7 @@ def validator(value: Any) -> list[T] | None:
         if value is None:
             return None
         if not isinstance(value, (list, tuple)):
-            return value  # type: ignore[return-value]
+            return value  # type: ignore
         result: list[T] = []
         for item in value:
             if isinstance(item, enum_class):
@@ -92,9 +92,9 @@ def validator(value: Any) -> list[T] | None:
                     result.append(enum_class(item))
                 except ValueError:
                     # Let Pydantic handle the validation error
-                    result.append(item)  # type: ignore[arg-type]
+                    result.append(item)  # type: ignore
             else:
-                result.append(item)  # type: ignore[arg-type]
+                result.append(item)
         return result
 
     return validator
@@ -131,7 +131,7 @@ def validator(value: Any) -> M | None:
             return value
         if isinstance(value, dict):
             return model_class(**value)
-        return value  # type: ignore[return-value]
+        return value  # type: ignore
 
     return validator
 
@@ -170,7 +170,7 @@ def validator(value: Any) -> list[M] | None:
         if value is None:
             return None
         if not isinstance(value, (list, tuple)):
-            return value  # type: ignore[return-value]
+            return value  # type: ignore
         # Return the list as-is - Pydantic will validate each item
         # is an instance of base_class (including subclasses)
         return list(value)