Preserve input float dtype through resample() (#1467)

[brendancol]

Summary

• resample() picks its working dtype from the input instead of forcing float64 in / float32 out. float64 in keeps float64; float32 in keeps float32; integer / bool in returns float32 (NaN-sentinel resampling needs a float type).
• All four backend runners (numpy, cupy, dask+numpy, dask+cupy) and their block helpers thread the working/output dtypes through.
• Aggregation kernels (numba @ngjit) keep a hardcoded float64 accumulator internally; the runner casts the result to the output dtype at the end. That keeps existing float32 aggregation accuracy and avoids re-specialising the kernels.

Closes #1467.

Test plan

• float64 input gives float64 output, values match a float64 reference (atol=1e-12).
• float32 input gives float32 output (existing default).
• int16/int32/int64/uint8/uint16 input gives float32 output.
• dask paths follow the same dtype rules (numpy backend).
• int + nodata sentinel path is gated on the nodata parameter being present and skips otherwise (will activate once that parameter lands).
• Existing 62 resample tests still pass.

[brendancol]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved. The merge with origin/main introduced two sets of conflicts:

1. xrspatial/resample.py — _agg_block_np: kept the out_dtype parameter from this branch and the faster inlined numba kernels (_AGG_BLOCK_FUNCS) that landed in main. Also fixed _apply_nodata_mask to promote integer inputs to float32 (not float64) so the integer→float32 dtype rule stays consistent.

2. xrspatial/tests/test_resample.py — kept both the TestDtypePreservation tests from this branch and the TestDaskAggregateInlined, TestThreeDRasters, TestNodata test classes from main. Removed a duplicate TestTargetResolutionTuple class that appeared twice after the merge. Also corrected the sentinel position in test_int_input_with_nodata_propagates_nan to land on a pixel that nearest-neighbour actually samples.

All 112 tests pass (commit f67015d).

[brendancol]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved again (commit 4b27684). The new conflicts came from two more commits that landed on main:

• xrspatial/resample.py — auto-merged cleanly: updated the cubic depth comment and tightened the NaN weight threshold from 0.01 → 0.5.
• xrspatial/tests/test_resample.py — kept TestDtypePreservation from this branch and merged in the four new test classes from main (TestCoordinateOrientation, TestInfHandling, TestDimensionRejection, TestReproducibility).

All 127 tests pass.