chore: drop Python 3.9, set 3.10 as minimum

[bhimrazy]

What does this PR do?

Drops Python 3.9 support and bumps the minimum supported version to Python 3.10 across the entire repo.

Also closes #3320

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

---

📚 Documentation preview 📚: https://torchmetrics--3330.org.readthedocs.build/en/3330/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 37%. Comparing base (4d52812) to head (5317f70).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #3330    +/-   ##
=======================================
- Coverage      37%     37%    -1%     
=======================================
  Files         364     349    -15     
  Lines       20099   19903   -196     
=======================================
- Hits         7521    7327   -194     
+ Misses      12578   12576     -2     

🚀 New features to boost your workflow:

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