fix: build and ci

[nicrie]

• add statsmodels as dependency
• remove support for python 3.9
• fix test cases for MCA

[codecov-commenter]

Codecov Report

Merging #45 (4e33e86) into main (1e1694f) will decrease coverage by 4.83%.
The diff coverage is 91.49%.

@@            Coverage Diff             @@
##             main      #45      +/-   ##
==========================================
- Coverage   96.28%   91.45%   -4.83%     
==========================================
  Files          49       39      -10     
  Lines        3206     2599     -607     
==========================================
- Hits         3087     2377     -710     
- Misses        119      222     +103     

Impacted Files	Coverage Δ
xeofs/utils/rotation.py	88.67% <ø> (-5.67%)	⬇️
xeofs/utils/sanity_checks.py	80.76% <ø> (ø)
xeofs/utils/statistics.py	68.00% <ø> (ø)
xeofs/utils/xarray_utils.py	94.73% <ø> (ø)
xeofs/validation/__init__.py	100.00% <ø> (ø)
xeofs/validation/bootstrapper.py	98.59% <ø> (ø)
xeofs/models/mca_rotator.py	58.63% <58.44%> (-39.78%)	⬇️
xeofs/models/_base_model.py	75.00% <75.00%> (ø)
xeofs/preprocessing/_base_stacker.py	76.19% <76.19%> (ø)
xeofs/preprocessing/_base_scaler.py	84.21% <84.21%> (ø)
... and 29 more