python 3.15 compat

[bckohan]

No description provided.

[Copilot]

Pull request overview

Updates the project to explicitly support and validate compatibility with Python 3.15 by expanding CI coverage and adding targeted tests for new/changed stdlib enum behavior introduced in 3.15.

Changes:

• Add Python 3.15 Trove classifier in project metadata.
• Extend GitHub Actions test and lint matrices to include Python 3.15 (with prereleases allowed).
• Add Python 3.15–gated tests covering new public enum APIs (show_flag_values, bin) and updated IntFlag negative-value inversion behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/annotations/test_flags.py	Adds Python 3.15–specific tests for new enum APIs and changed IntFlag semantics relevant to this library.
pyproject.toml	Declares Python 3.15 support via Trove classifier.
.github/workflows/test.yml	Runs the test suite on Python 3.15 across Linux/macOS/Windows.
.github/workflows/lint.yml	Runs static analysis on Python 3.15 as the new “bleeding edge” version.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b98a07f) to head (1fd6897).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #170   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          414       414           
  Branches        85        85           
=========================================
  Hits           414       414           

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