Release v3.1.2 with Python 3.14 type annotation fix

[Copilot]

Bump version from 3.2.0.dev0 to 3.1.2 for bugfix release.

Changes

• Updated __version__ in cloudpickle/__init__.py to 3.1.2

Release notes

Per CHANGES.md, this release fixes pickling of classes containing type annotations for Python 3.14 (PR#578).

Original prompt

Prepare a PR for a bugfix release based on the contents of the changelog. Don't forget to update the version number in the module's init.py.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.34%. Comparing base (6ff1cc2) to head (204c19b).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #579   +/-   ##
=======================================
  Coverage   96.34%   96.34%           
=======================================
  Files           3        3           
  Lines         575      575           
  Branches      121      121           
=======================================
  Hits          554      554           
  Misses         11       11           
  Partials       10       10           

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