Add an error conversion impl for `NormalBroadcast` #165

Job	Run time
build-docs	32s
clippy	27s
rustfmt	9s
semver	30s
stable-test (x86_64-unknown-linux-gnu, 1.81.0)	41s
test-and-coverage	47s
wasm-build (1.81.0, wasm32-unknown-unknown)	23s
wasm-build (stable, wasm32-unknown-unknown)	19s
	3m 48s

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