Use scanpy for reading matrixes

[cgeyskens]

Changes made related to issue #228

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 61.81%. Comparing base (86e789f) to head (8c5ba82).

Files with missing lines	Patch %	Lines
src/spatialdata_io/readers/_utils/_utils.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #292      +/-   ##
==========================================
- Coverage   62.15%   61.81%   -0.34%     
==========================================
  Files          27       26       -1     
  Lines        3181     3135      -46     
==========================================
- Hits         1977     1938      -39     
+ Misses       1204     1197       -7     

Files with missing lines	Coverage Δ
src/spatialdata_io/readers/xenium.py	74.93% <100.00%> (+0.38%)	⬆️
src/spatialdata_io/readers/_utils/_utils.py	47.87% <66.66%> (-0.55%)	⬇️

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[LucaMarconato]

Thanks @cgeyskens, this PR simplifies the codebase.

I updated xenium.py because https://github.com/scverse/spatialdata-io/pull/312/changes introduced some Xenium-specific differences from the scanpy implementation. Now those changes are local to the Xenium reader also in the code.