Make `Round` dyn-safe #219

Job	Run time
rustfmt	4s
build-docs	38s
clippy	26s
semver	16s
stable-test (x86_64-unknown-linux-gnu, 1.81.0)	41s
test-and-coverage	58s
wasm-build (1.81.0, wasm32-unknown-unknown)	23s
wasm-build (stable, wasm32-unknown-unknown)	26s
	3m 52s

Provide feedback