Refactor: Add type hints to CodeParser AST visitor methods

[pyob-bot]

Summary of Changes

This PR introduces explicit type annotations to the CodeParser class methods within src/pyob/pyob_code_parser.py. Specifically, it updates the ast visitor methods (visit_ImportFrom, visit_ClassDef, visit_FunctionDef, visit_AsyncFunctionDef) and the helper method handle_function to include proper type hints for ast nodes and return types.

Technical Impact

• Improved Type Safety: By explicitly defining the expected ast node types, the code is now more resilient to type-related bugs and better supported by static analysis tools like mypy or pyright.
• Enhanced Maintainability: The addition of type hints improves code readability and provides better IDE autocompletion and documentation for developers working on the parser.
• No Functional Changes: This is a non-breaking refactor; the logic remains identical to the previous implementation.