Rust

[WIP] first part of moving to Tokio #290

Job	Run time
linting	47s
cross-testing (stable, ubuntu-latest)	1m 23s
build	2m 23s
cross-testing (stable, windows-latest)	2m 45s
cross-testing (stable, macos-latest)	3m 47s
cross-testing (nightly, ubuntu-latest)	1m 24s
cross-testing (nightly, windows-latest)	3m 24s
cross-testing (nightly, macos-latest)	4m 36s
cross-testing (1.64, ubuntu-latest)	1m 25s
cross-testing (1.64, windows-latest)	3m 58s
cross-testing (1.64, macos-latest)	3m 6s
	28m 58s

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