Add `Variable::chunking` #346

Job	Run time
Address sanitizer	1m 23s
mpi-runner	1m 24s
rustfmt	1m 9s
test apt (stable)	48s
conda (ubuntu, conda-forge, stable)	52s
static builds (ubuntu-latest, stable)	1m 26s
test apt (beta)	40s
conda (windows, conda-forge, stable)	2m 47s
static builds (windows-latest, stable-msvc)	5m 43s
test apt (nightly)	37s
conda (macos, conda-forge, stable)	1m 0s
static builds (windows-latest, stable-gnu)	6m 0s
static builds (macos-12, stable)	3m 7s
static builds (macos-latest, stable)	1m 39s
	28m 35s

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