`Send`/`Sync` adjustment #206

Job	Run time
build-docs	35s
rustfmt	8s
clippy	29s
semver	18s
stable-test (x86_64-unknown-linux-gnu, 1.81.0)	44s
test-and-coverage	40s
wasm-build (1.81.0, wasm32-unknown-unknown)	23s
wasm-build (stable, wasm32-unknown-unknown)	19s
	3m 36s

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