`Send`/`Sync` adjustment #205

Job	Run time
rustfmt	3s
clippy	29s
build-docs	32s
semver	23s
stable-test (x86_64-unknown-linux-gnu, 1.81.0)	46s
test-and-coverage	49s
wasm-build (1.81.0, wasm32-unknown-unknown)	23s
wasm-build (stable, wasm32-unknown-unknown)	16s
	3m 41s

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