Python: separate compute functions into `geoarrow.rust.compute` module #1868

Job	Run time
Lint and Test	3m 8s
build-benchmarks	2m 55s
check-features-with-external-dependencies (-F gdal -F gdal/bindgen)	48s
check-features	25s
check-features-with-external-dependencies (-F geos)	33s
check-features (-F csv)	24s
check-features-with-external-dependencies (-F proj)	53s
check-features (-F flatgeobuf)	23s
check-features (-F flatgeobuf_async)	47s
check-features (-F geozero)	25s
check-features (-F ipc_compression)	36s
check-features (-F parquet)	26s
check-features (-F parquet_async)	32s
check-features (-F parquet_compression)	30s
check-features (-F polylabel)	28s
check-features (-F postgis)	37s
check-features (-F rayon)	23s
	14m 13s

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