Fix dtype issue with bbox in SQLGraph

[yfukai]

For some cases the bbox column of SQLGraph becomes "pl.List" dtype, causing index out of range error. This is a tentative fix for this issue. After we implement #193 we will be able to remove this cast safely.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.25%. Comparing base (e87a375) to head (4195520).

Files with missing lines	Patch %	Lines
src/tracksdata/graph/filters/_spatial_filter.py	75.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #212      +/-   ##
==========================================
- Coverage   88.29%   88.25%   -0.04%     
==========================================
  Files          53       53              
  Lines        3809     3815       +6     
  Branches      661      662       +1     
==========================================
+ Hits         3363     3367       +4     
- Misses        266      267       +1     
- Partials      180      181       +1     

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[JoOkuma]

Thanks @yfukai , LGTM.
Can I merge this?

[yfukai]

Thanks, yes! @JoOkuma