Summary

Adds Python 3.14 support by cherry-picking upstream fix python-lsp/python-lsp-server#690 (44f7eb0).

On Python 3.14, the server crashes when a client connects in TCP mode (the mode Deepnote uses):

TypeError: PythonLSPServer.init() got multiple values for argument 'check_parent_process'

This happens because functools.partial changed in 3.14. The fix wraps DELEGATE_CLASS in staticmethod on 3.14+ only. Older versions don't change.

Changes

• pylsp/python_lsp.py: 3.14-only staticmethod(partial(...)) wrapper for DELEGATE_CLASS
• CI test matrices: Linux 3.9–3.14; macOS/Windows 3.9, 3.12, 3.14
• test/plugins/test_flake8_lint.py: use a Windows-compatible config path in the test

Cherry-picked unchanged (-x), so the commit matches upstream's.

No breaking changes

• No dependency changes. jedi 0.19.2, parso 0.8.7 and pylint 3.3.x install on 3.14 within the current version limits.
• requires-python is still >=3.9.
• Deepnote-specific behaviour (TCP auth, hover format, completion_detail) is untouched.

Testing

• Full test suite: 188 passed, 18 skipped on both 3.14 and 3.9. The one error (test_language_server.py::test_missing_message teardown) is also on develop and on 3.11, so it isn't caused by this PR.
• Manual: on 3.14, pylsp --tcp authenticates and answers initialize. Before this fix it crashed on connect.

Summary by CodeRabbit

• Compatibility

  • Improved TCP language-server startup compatibility with Python 3.14 and later; earlier Python versions retain their existing behavior.

• Testing

  • Linux test coverage now includes Python 3.12–3.14 in addition to 3.9–3.11.
  • macOS and Windows test coverage now targets Python 3.9, 3.12, and 3.14.
  • Updated Flake8 configuration-path testing to account for Windows-style paths.

Contributes to BLU-6474