build: drop python 3.9 and pyside2, support python 3.14

[tlambert03]

cc @jni and @Czaki

this doesn't explicitly break pyside2, but we won't be testing it going forward

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.03%. Comparing base (c5b02dc) to head (21c4b6f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@ ## main #332 +/- ## ========================================== + Coverage 86.37% 87.03% +0.65%  ========================================== Files 49 49 Lines 3869 3864 -5 ========================================== + Hits 3342 3363 +21  + Misses 527 501 -26 

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[Czaki]

We dropped pyside2 in napari too. The only problem might be a person installing older napari release, but we provide constraints files from a log time so maybe we need more documentation only.