Update dependencies and CI configuration

[GitBib]

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Description

This pull request updates the following:

• Bumps pymkv2 to version 2.1.2 for compatibility and improvements.
• Adjusts pytest-cov version range to align with the latest standards.
• Adds Python 3.14 to the CI testing matrix for extended version compatibility testing.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.01%. Comparing base (d223bef) to head (be80aa6).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #82   +/-   ##
=======================================
  Coverage   67.01%   67.01%           
=======================================
  Files          10       10           
  Lines         958      958           
=======================================
  Hits          642      642           
  Misses        316      316           

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