Make `Round` dyn-safe #216

Job	Run time
clippy	27s
build-docs	32s
semver	2m 34s
rustfmt	5s
stable-test (x86_64-unknown-linux-gnu, 1.81.0)	42s
test-and-coverage	43s
wasm-build (1.81.0, wasm32-unknown-unknown)	24s
wasm-build (stable, wasm32-unknown-unknown)	20s
	5m 47s

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