Update Python version references to 3.13

[codegen-sh]

This PR updates all Python version references to consistently use Python 3.13 throughout the codebase.

Changes:

• Updated Dockerfile to use Python 3.13 for codecov-cli installation
• Updated Union type codemod to reference Python 3.13 instead of Python 3.10

This addresses the request to standardize on Python 3.13 across the codebase.

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