adjusted CellComposite and CellLabels loading in read_nanostring

[FrancescaDr]

Description

• instead of automatic loading of all fov it checks if the fov variables exists in CellCompositon and CellLabels, like has been done for metadata loading
• optional loading of .uns variables from CellComposition and CellLabels (not all CosmX nano string data has the information available, e.i. bowel disease data does not have CellLabels information )

How has this been tested?

Tested with two different patients from CosmX Lung (test/test_nanostring.py) and loading with data from CosmX bowel disease data

Closes

closes #585

[giovp]

hi @FrancescaDr could you please rebase from main ? it should fix tests. Also could you remove the tests for the reader? after that we can merge it!

[codecov-commenter]

Codecov Report

Merging #766 (6f48274) into main (c528ce7) will decrease coverage by 0.07%.
The diff coverage is 0.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #766      +/-   ##
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- Coverage   69.94%   69.87%   -0.07%     
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  Files          39       39              
  Lines        5476     5481       +5     
  Branches     1024     1025       +1     
==========================================
  Hits         3830     3830              
- Misses       1358     1363       +5     
  Partials      288      288              

Files	Coverage Δ
src/squidpy/read/_read.py	35.86% <0.00%> (-2.07%)	⬇️