Add Python 3.14 to CI matrix, drop 3.8

[Copilot]

Adds Python 3.14 to the test matrix, removes 3.8 (EOL), and switches coverage reporting to run on 3.14.

Changes

• build.yml: Updated python-version matrix from [3.8, 3.9, 3.10, 3.11, 3.12, 3.13] → [3.9, 3.10, 3.11, 3.12, 3.13, 3.14]
• build.yml: Updated PYTHON_COVREPORTS_VERSION from 3.13 → 3.14
• setup.py: No changes required — no version classifiers or python_requires referencing 3.8

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.78%. Comparing base (0fc2b9d) to head (2a99403).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #38   +/-   ##
=======================================
  Coverage   98.78%   98.78%           
=======================================
  Files           1        1           
  Lines          82       82           
=======================================
  Hits           81       81           
  Misses          1        1           

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