Struct attrributes

[yfukai]

Partially solves #194 by allowing pl.Struct saved and searched in graphs.
Assumes #262 merged.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 76.11465% with 75 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.02%. Comparing base (e4bb183) to head (19055ab).

Files with missing lines	Patch %	Lines
src/tracksdata/graph/_sql_graph.py	80.12%	20 Missing and 13 partials ⚠️
src/tracksdata/utils/_dtypes.py	72.60%	11 Missing and 9 partials ⚠️
src/tracksdata/attrs.py	72.72%	10 Missing and 2 partials ⚠️
src/tracksdata/graph/_rustworkx_graph.py	56.52%	8 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #268      +/-   ##
==========================================
- Coverage   87.92%   87.02%   -0.90%     
==========================================
  Files          56       56              
  Lines        4471     4741     +270     
  Branches      789      844      +55     
==========================================
+ Hits         3931     4126     +195     
- Misses        344      395      +51     
- Partials      196      220      +24     

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[yfukai]

Maybe I should save the data field-wise in SQLGraph. Let me experiment in this way.

[JoOkuma]

@yfukai, let me know when this is ready for review.