Replication of original PR #595: Become robust to things being removed from typing

[yashwanthatla]

PR Summary

Improve typing aliases import mechanism for better Python version compatibility

Overview

This PR changes how typing aliases are imported from the typing module to use dynamic imports with hasattr() checks, improving compatibility with future Python versions. It also adds tests to verify all typing names remain accessible.

Change Types

Type	Description
Enhancement	Improved import mechanism for typing aliases
Test	Added test to verify typing name accessibility

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Affected Modules

Module / File	Change Description
typing_extensions.py	Changed to dynamic imports with hasattr() checks
test_typing_extensions.py	Added test for typing name accessibility

Notes for Reviewers

• The change to dynamic imports should maintain backward compatibility while improving future compatibility
• Verify the new test correctly validates all typing names are accessible