Rust

Bump version to 21.1.0 #397

Job	Run time
fmt	12s
build-and-test (msrv)	2m 48s
build-and-test (latest)	1m 58s
publish-dry-run (ubuntu-latest, x86_64-unknown-linux-gnu, --feature-powerset) / publish-dry-run	1m 0s
publish-dry-run (ubuntu-latest, aarch64-unknown-linux-gnu, --feature-powerset) / publish-dry-run	1m 27s
publish-dry-run (windows-latest-8-cores, x86_64-pc-windows-msvc) / publish-dry-run	2m 34s
publish-dry-run (windows-latest-8-cores, x86_64-pc-windows-msvc, --features opt --ignore-unknown-... / publish-dry-run	3m 14s
complete	1s
	13m 14s

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