Add Visium ingestor and sample spatial notebook

[jp-dark]

• Adds an experimental Visium ingestor.
• Adds an example notebook for the spatial support.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 274 lines in your changes missing coverage. Please review.

Project coverage is 82.05%. Comparing base (0a9bf28) to head (dc5ec3e).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3123      +/-   ##
==========================================
- Coverage   86.56%   82.05%   -4.52%     
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  Files          47       50       +3     
  Lines        4920     5198     +278     
==========================================
+ Hits         4259     4265       +6     
- Misses        661      933     +272     

Flag	Coverage Δ
python	82.05% <0.00%> (-4.52%)	⬇️

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Components	Coverage Δ
python_api	82.05% <0.00%> (-4.52%)	⬇️
libtiledbsoma	∅ <ø> (∅)