fix: support raster labels above uint16

[stanbot8]

2 implementations exist. This implementation uses 1 canvas and only removes the label-count limit. The other implementation adds opt-in output tiles after this commit to limit output memory. Compare the limitations.

Summary

In issue 987, rasterize(..., return_regions_as_labels=True) rejects more than 65,535 labels. Select the output dtype from the maximum label. Closes #987.

Design

Use the existing _get_uint_dtype() helper, as proposed in the maintainer direction. Small outputs remain uint16. Larger outputs use uint32 or uint64 only when required.

The implementation changes src/spatialdata/_core/operations/rasterize.py.

Limitations

This implementation uses 1 canvas. It removes the label-count limit, but it does not bound output memory.

Tests

1 boundary test rasterizes 65,536 indexed points. It preserves label 65,536 in uint32 output.

The focused rasterization suites pass with 28 tests. The complete suite passes with 1,365 tests, 7 skips, and 1 expected failure. An isolated installed wheel passes the same boundary case.

The test is in tests/core/operations/test_rasterize.py.

Commands

uv run pytest tests/core/operations/test_rasterize.py::test_rasterize_points_selects_label_dtype -q

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.47%. Comparing base (eb4fb3d) to head (72250aa).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1167      +/-   ##
==========================================
+ Coverage   92.44%   92.47%   +0.03%     
==========================================
  Files          51       51              
  Lines        7820     7817       -3     
==========================================
  Hits         7229     7229              
+ Misses        591      588       -3     

Files with missing lines	Coverage Δ
src/spatialdata/_core/operations/rasterize.py	90.84% <100.00%> (+0.24%)	⬆️

... and 1 file with indirect coverage changes

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