drop python 3.9 support

[bigcat88]

Before adding support for Async, we remove Python 3.9 support in order to reduce the amount of work later, since support for asynchrony will add a lot of duplicate code.

I do this with pain in my heart

[codecov]

Codecov Report

Merging #180 (d3470aa) into main (9eed252) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #180      +/-   ##
==========================================
- Coverage   99.84%   99.84%   -0.01%     
==========================================
  Files          36       36              
  Lines        3277     3260      -17     
==========================================
- Hits         3272     3255      -17     
  Misses          5        5              

Files	Coverage Δ
nc_py_api/_misc.py	100.00% <100.00%> (ø)
nc_py_api/_preferences_ex.py	100.00% <100.00%> (ø)
nc_py_api/_session.py	99.13% <100.00%> (ø)
nc_py_api/_talk_api.py	100.00% <100.00%> (ø)
nc_py_api/_version.py	100.00% <100.00%> (ø)
nc_py_api/activity.py	100.00% <ø> (ø)
nc_py_api/apps.py	100.00% <100.00%> (ø)
nc_py_api/ex_app/integration_fastapi.py	100.00% <ø> (ø)
nc_py_api/ex_app/misc.py	100.00% <100.00%> (ø)
nc_py_api/ex_app/ui/files_actions.py	100.00% <100.00%> (ø)
... and 16 more