feat: add opt-in rasterization tiles

[stanbot8]

Summary

A large rasterization canvas can exceed available memory. Compute tiled raster shape and fill metadata 1 time before tile graph construction. Closes #987.

Design

The rasterization path can create 1 output canvas for the complete target extent. An enabled tile size bounds each rasterization canvas and preserves output coordinates and tile boundaries.

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

Limitations

• Tiling is opt-in.
• Smaller tiles create more tasks.

Tests

The baseline failed, and the candidate passed the same reproducer. The focused A/B reproducer passed on the candidate. The upstream CI test matrix passed. The repository quality checks passed in CI.

The tests are in tests/core/operations/test_rasterize.py.

Commands

python -m pytest tests/core/operations/test_rasterize.py -q
ruff check src/spatialdata/_core/operations/rasterize.py tests/core/operations/test_rasterize.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.55%. Comparing base (eb4fb3d) to head (6d80ac6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1166      +/-   ##
==========================================
+ Coverage   92.44%   92.55%   +0.11%     
==========================================
  Files          51       51              
  Lines        7820     7901      +81     
==========================================
+ Hits         7229     7313      +84     
+ Misses        591      588       -3     

Files with missing lines	Coverage Δ
src/spatialdata/_core/operations/rasterize.py	92.87% <100.00%> (+2.27%)	⬆️

... and 1 file with indirect coverage changes

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