Support rechunking to a frequency. #12892

Job	Run time
detect ci trigger	3s
Event File	3s
ubuntu-latest py3.9	7m 28s
ubuntu-latest py3.12	9m 11s
macos-latest py3.9	5m 18s
macos-latest py3.12	5m 44s
windows-latest py3.9	12m 26s
windows-latest py3.12	12m 23s
ubuntu-latest py3.9 bare-minimum	1m 33s
ubuntu-latest py3.9 min-all-deps	6m 14s
ubuntu-latest py3.11 all-but-dask	6m 8s
ubuntu-latest py3.12 flaky	1m 40s
	1h 8m 11s

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