Drop python 3.9

[mraspaud]

This PR drops support for python 3.9, as deemed reasonable in #2741. This superseeds #2741 which was difficult to merge with main.
Also, we added an experimental build for python 3.13.

• Closes Drop Python 3.9 support #2741

[pnuu]

LTGM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.09%. Comparing base (5634073) to head (f9dccad).
Report is 77 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #2936    +/-   ##
========================================
  Coverage   96.08%   96.09%            
========================================
  Files         375      377     +2     
  Lines       54615    55075   +460     
========================================
+ Hits        52478    52925   +447     
- Misses       2137     2150    +13     

Flag	Coverage Δ
behaviourtests	3.95% <ø> (-0.04%)	⬇️
unittests	96.19% <ø> (+<0.01%)	⬆️

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[mraspaud]

hmm, looks like the 3.13 experimental was a bad idea...

[coveralls]

Pull Request Test Coverage Report for Build 11384578870

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 6 unchanged lines in 5 files lost coverage.
• Overall coverage decreased (-0.01%) to 96.202%

---

Files with Coverage Reduction	New Missed Lines	%
satpy/readers/file_handlers.py	1	97.4%
satpy/readers/sgli_l1b.py	1	95.17%
satpy/readers/xmlformat.py	1	88.79%
satpy/tests/reader_tests/test_ahi_hsd.py	1	99.34%
satpy/readers/pmw_channels_definitions.py	2	96.41%

Totals
Change from base Build 11381112172:	-0.01%
Covered Lines:	53169
Relevant Lines:	55268

---

💛 - Coveralls

[djhoese]

Were all the FCI/decomp requirements/requests related to dropping Python 3.9 resolved?

[mraspaud]

Yes I think so

[mraspaud]

The last comment on #2741 confirms it.