fix: update Python 3 compatibility for setup.py and tests

[lyushher]

Summary

This PR improves Python 3 compatibility by updating CaseInsensitiveDict.copy(), relaxing the version parsing regex in setup.py, replacing legacy py2exe package names, and adding tests for the updated behavior.

Changes

• Update CaseInsensitiveDict.copy() to construct a new instance from a dict instead of a raw dict_values view.
• Fix the serializable typo in the CaseInsensitiveDict comment.
• Relax the version parsing regex in setup.py to support flexible whitespace around =.
• Replace legacy Python 2 py2exe package names with their Python 3 equivalents (http.client, html.parser, and configparser).
• Add unit tests covering the updated version parsing, Python 3 package names, and CaseInsensitiveDict.copy() behavior.

Testing

python -m pytest tests/unit/test_setup.py tests/unit/test_tests_init.py -v
python setup.py --version

All added tests passed.

Fixes #10492