chore: release 2.3.1

[GitBib]

Summary

• Bumps version to 2.3.1.

Patch release picking up the post-2.3.0 fixes:

• fix: conditional Self import depending on python version #111 — declare typing-extensions as a runtime dependency on Python < 3.11 and use stdlib typing.Self on 3.11+ (fixes the ModuleNotFoundError on import pymkv for runtime-only installs).
• ci: add runtime-only import smoke test #112 — CI smoke job that imports the package without dev dependencies, to catch this class of regression in the future.

Test plan

• CI green on master matrix.
• Runtime-only import smoke job passes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.11%. Comparing base (8638b81) to head (a268157).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #113   +/-   ##
=======================================
  Coverage   99.11%   99.11%           
=======================================
  Files          21       21           
  Lines        1475     1475           
=======================================
  Hits         1462     1462           
  Misses         13       13           

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