feat: add support for non-gex data in visium hd

[stephenwilliams22]

Sets the default for the read_10x_h5 function gex_only parameter value to False.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.65%. Comparing base (487803d) to head (bebce8a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #391   +/-   ##
=======================================
  Coverage   61.65%   61.65%           
=======================================
  Files          27       27           
  Lines        3161     3161           
=======================================
  Hits         1949     1949           
  Misses       1212     1212           

Files with missing lines	Coverage Δ
src/spatialdata_io/readers/visium_hd.py	75.16% <100.00%> (ø)

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