perf: accelerate crop raster aggregation

[koen-vg]

Summary

• precompute exact region, resource-class, and raster-cell coverage once per configuration
• reuse that mapping for vectorized crop-yield and harvested-area aggregation while retaining one crop/water-supply per Snakemake job
• validate raster shape, transform, and CRS against the cached mapping
• reduce rule memory requests and document the shared intermediate artifact
• add focused tests for fractional polygon coverage and empty-group behavior

Performance

On the full-resolution central wheat-irrigated case, pinned to one core:

• crop yields: about 11 s and 879 MB peak RSS -> about 1.2 s and 320 MB
• harvested area: about 2.8 s and 477 MB peak RSS -> about 0.7 s and 299 MB
• one-time mapping build: about 1-2.5 s and 300 MB peak RSS (18 MB artifact)

This is about 9x faster with 64% less peak memory for crop yields, and about 4x faster with 37% less peak memory for harvested area. The mapping cost is amortized across all crop and water-supply jobs in a configuration.

Correctness

Optimized CSVs are byte-identical to the baseline for:

• irrigated potential wheat
• rainfed actual wheat
• irrigated potential sugarcane, including its unit-conversion override
• irrigated wheat harvested area
• rainfed alfalfa harvested area, including the fodder aggregate
• rainfed olive harvested area, including the oil-crop deflation
• rainfed banana harvested area, including the fruit residual

The implementation retains exact fractional polygon coverage. A center-cell region mapping was rejected because it materially changes boundary allocation.

Batching crops into fewer Snakemake jobs was also rejected: after removing the repeated spatial work, independent jobs are faster in aggregate under normal parallel execution and retain finer failure, scheduling, and invalidation granularity.

Validation

• pytest -q tests/test_region_class_aggregation.py (5 passed)
• pytest -q tests/test_integration.py::test_workflow_dryrun
• byte-for-byte comparisons for representative yield and harvested-area outputs
• ruff, formatting, snakefmt, REUSE, Sphinx warnings-as-errors, and repository hooks