Cuda and cuda-with-dask support for inspection reductions

[ianthomas23]

This implements CUDA and CUDA-with-Dask support for the inspection reductions first, first_n, last and last_n, as well as the same reductions wrapped in a where reduction e.g. where(first_n("value", n=3), "other").

Closes #1182 and #1207.

This is implemented on top of #1217; ideally that would be merged before this to keep the commits separate.

[codecov]

Codecov Report

Merging #1219 (3470fba) into main (fc82f8e) will decrease coverage by 1.03%.
The diff coverage is 34.92%.

@@            Coverage Diff             @@
##             main    #1219      +/-   ##
==========================================
- Coverage   84.63%   83.61%   -1.03%     
==========================================
  Files          35       35              
  Lines        8600     8734     +134     
==========================================
+ Hits         7279     7303      +24     
- Misses       1321     1431     +110     

Impacted Files	Coverage Δ
datashader/utils.py	81.53% <ø> (-0.33%)	⬇️
datashader/transfer_functions/_cuda_utils.py	20.63% <13.95%> (-1.97%)	⬇️
datashader/reductions.py	79.24% <36.76%> (-4.37%)	⬇️
datashader/compiler.py	88.35% <100.00%> (+0.44%)	⬆️

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