chore: upgrade Python matrix in CI

[alespour]

3.8 EOL-ed in 2024! This PR

• upgrades default to 3.9
• adds 3.14 to matrix

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.17%. Comparing base (a055a0a) to head (7091011).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #199      +/-   ##
==========================================
+ Coverage   71.53%   75.17%   +3.64%     
==========================================
  Files          35       35              
  Lines        2417     2417              
==========================================
+ Hits         1729     1817      +88     
+ Misses        688      600      -88     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[bednar]

The README also contains version of the Python, please align version also there.

[Copilot]

Pull request overview

Updates the project’s supported Python versions by dropping 3.8 and moving the baseline/test matrix forward to newer runtimes, aligning packaging metadata, documentation, and CI.

Changes:

• Bump minimum supported Python from 3.8 to 3.9 in packaging metadata.
• Update CircleCI default image to Python 3.9 and extend the test matrix to include 3.14.
• Remove unnecessary global declarations in tests and update README’s Python version note.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/util/mocks.py	Removes an unnecessary global used only for reading a module variable.
tests/test_api_client.py	Removes unnecessary global _package declarations in tests.
setup.py	Raises python_requires to >=3.9 and updates supported-version classifiers (adds 3.14).
README.md	Updates documented minimum Python version to 3.9+.
.circleci/config.yml	Switches default Python image to 3.9 and adds Python 3.14 to the CI matrix.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[bednar]

LGTM 🚀