einops accessor

[OriolAbril]

Homogenize einops API and add accessors for einops and linalg (a subset of functions that have a
single argument or a clear main argument).

Ref pydata/xarray#7295

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📚 Documentation preview 📚: https://xarray-einstats--51.org.readthedocs.build/en/51/

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[codecov]

Codecov Report

Merging #51 (b03640c) into main (2b92d28) will decrease coverage by 0.62%.
The diff coverage is 90.51%.

@@            Coverage Diff             @@
##             main      #51      +/-   ##
==========================================
- Coverage   91.02%   90.40%   -0.62%     
==========================================
  Files           6        6              
  Lines         713      782      +69     
==========================================
+ Hits          649      707      +58     
- Misses         64       75      +11     

Impacted Files	Coverage Δ
src/xarray_einstats/einops.py	88.05% <86.66%> (-1.82%)	⬇️
src/xarray_einstats/linalg.py	91.96% <88.88%> (-0.97%)	⬇️
src/xarray_einstats/accessors.py	92.85% <92.85%> (ø)
src/xarray_einstats/__init__.py	94.59% <100.00%> (+0.15%)	⬆️

... and 1 file with indirect coverage changes