[wip] Support arrow-backed pandas categorical columns. #16099

Job	Run time
Build CUDA + manylinux_2_28_x86_64 wheel	12m 9s
Build CPU	14m 43s
Build CUDA with RMM	13m 59s
Build manylinux_2_28_aarch64 wheel	4m 26s
Build CUDA with RMM (dev)	13m 30s
Build CPU wheel for manylinux2014_x86_64	2m 19s
Build GPU-enabled R package	24m 45s
Build CPU wheel for manylinux2014_aarch64	2m 19s
Build CPU wheel for manylinux_2_28_x86_64	1m 51s
Build CPU wheel for manylinux_2_28_aarch64	2m 48s
Run Python tests (multiple-gpu)	20m 17s
Run Python tests (single-gpu)	19m 39s
Run Python tests (cpu-arm64)	1m 39s
Run Python tests (cpu-amd64)	8m 37s
Run Google Tests with GPUs (Suite gpu-rmm, Runner linux-amd64-gpu)	5m 8s
Run Google Tests with GPUs (Suite mgpu, Runner linux-amd64-mgpu)	3m 1s
Run Google Tests with GPUs (Suite gpu, Runner linux-amd64-gpu)	5m 1s
	2h 36m 11s

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