Allow overriding scale_factor in visium hd

[LucaMarconato]

Continuing working from #383, original PR from @Tobiaspk.

[LucaMarconato]

@Tobiaspk thanks for opening the original PR. I made some changes since I wanted to avoid the .pop(), which would have otherwise modified the input from the user. The new approach makes a copy and leaves the user's input unaltered.

Also, I documented the usage of scale_factors in the docstring.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 61.85%. Comparing base (433014e) to head (7b8d24c).
⚠️ Report is 30 commits behind head on main.

Files with missing lines	Patch %	Lines
src/spatialdata_io/readers/visium_hd.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #394      +/-   ##
==========================================
+ Coverage   61.65%   61.85%   +0.19%     
==========================================
  Files          27       26       -1     
  Lines        3161     3138      -23     
==========================================
- Hits         1949     1941       -8     
+ Misses       1212     1197      -15     

Files with missing lines	Coverage Δ
src/spatialdata_io/readers/visium_hd.py	75.41% <80.00%> (+0.24%)	⬆️

... and 4 files with indirect coverage changes

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