Drop python 3.9, add 3.14

[jlaehne]

• Align python versions supported by LumiSpy to HyperSpy: Drop python3.9 hyperspy/hyperspy#3573
• Python 3.9 is end of life.
• Fixes azure pipelines, which were still running on 3.8!

Progress of the PR

• Change implemented (can be split into several points),
• docstring updated (if appropriate),
• add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:lumispy build of this PR (link in github checks),
• ready for review.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (8b64b0c) to head (f247eae).
⚠️ Report is 20 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff     @@
##   main   #247   +/-   ##
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