Support rechunking to a frequency. #12898

Job	Run time
detect ci trigger	3s
Event File	2s
ubuntu-latest py3.9	7m 32s
ubuntu-latest py3.12	9m 50s
macos-latest py3.9	5m 17s
macos-latest py3.12	6m 39s
windows-latest py3.9	16m 5s
windows-latest py3.12	18m 25s
ubuntu-latest py3.9 bare-minimum	1m 32s
ubuntu-latest py3.9 min-all-deps	6m 10s
ubuntu-latest py3.11 all-but-dask	5m 59s
ubuntu-latest py3.12 flaky	1m 38s
	1h 19m 12s

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