Update supported Python versions to 3.12-3.14

[IgorTatarnikov]

Update the supported Python versions to 3.12-3.14, following SPEC 0.

• Bump requires-python to >=3.12
• Update the Python version classifiers and tool target versions
• Update the CI test matrix to Python 3.12-3.14 (other OSes on 3.14)

Tracked in brainglobe/BrainGlobe#98

This PR was opened by a script. Please check that CI passes on the new Python versions before merging.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.55%. Comparing base (60cf6b7) to head (a1acbac).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #475   +/-   ##
=======================================
  Coverage   88.55%   88.55%           
=======================================
  Files          27       27           
  Lines        1319     1319           
=======================================
  Hits         1168     1168           
  Misses        151      151           

☔ View full report in Codecov by Harness.
📢 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.