Bugfix: Allow overriding scale_factor in visium hd

[Tobiaspk]

Closes #382

Minimal, non-break change to allow users to override scale_factors in visium HD reader. Crashes currently.

[Tobiaspk]

Changed typing Mapping to MutableMapping, which supports the pop method. this issue was highlighted by mypy pre-commit.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.69%. Comparing base (433014e) to head (2696766).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #383      +/-   ##
==========================================
+ Coverage   61.65%   61.69%   +0.03%     
==========================================
  Files          27       27              
  Lines        3161     3164       +3     
==========================================
+ Hits         1949     1952       +3     
  Misses       1212     1212              

Files with missing lines	Coverage Δ
src/spatialdata_io/readers/visium_hd.py	75.41% <100.00%> (+0.24%)	⬆️

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