feat: add opt-in rasterization tiles

[stanbot8]

Draft. Text in square brackets becomes links in the submission.

Summary

A large rasterization canvas can exceed available memory. Compute tiled raster shape and fill metadata 1 time before tile graph construction. Closes [issue 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. 14 rasterization tests passed. Ruff passed for the changed source and test files.

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