Full accessor support

[ilia-kats]

Implement MuData acessors. These are similar to and build on AnnData accessors, but add an additional level for modalities. So it is now possible to e.g. do

from mudata.acc import A

acc = A.mod["rna"].obs["cell_type"]

mdata[acc]

[codecov]

Codecov Report

❌ Patch coverage is 87.56219% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.09%. Comparing base (de6f210) to head (2432894).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/mudata/acc/__init__.py	87.30%	24 Missing ⚠️
src/mudata/_core/mudata.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #158      +/-   ##
==========================================
- Coverage   91.53%   91.09%   -0.45%     
==========================================
  Files          10       11       +1     
  Lines        1619     1819     +200     
==========================================
+ Hits         1482     1657     +175     
- Misses        137      162      +25     

Files with missing lines	Coverage Δ
src/mudata/__init__.py	100.00% <100.00%> (ø)
src/mudata/_core/mudata.py	93.11% <87.50%> (-0.06%)	⬇️
src/mudata/acc/__init__.py	87.30% <87.30%> (ø)

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[ilan-gold]

Nice pretty clean!

[flying-sheep]

Looks pretty much perfect, nice job!