build

Fixed build with `bitround` or `zfp` features without `async` feature #124

Job	Run time
fmt	33s
test	1m 55s
build (stable, --features "")	44s
clippy	48s
build (stable, --all-features)	1m 59s
build (stable, --no-default-features)	34s
build (1.71, --features "")	50s
build (1.71, --all-features)	2m 6s
build (1.71, --no-default-features)	47s
build (beta, --features "")	55s
build (beta, --all-features)	1m 59s
build (beta, --no-default-features)	53s
build (nightly, --features "")	1m 8s
build (nightly, --all-features)	2m 2s
build (nightly, --no-default-features)	53s
	18m 6s

Provide feedback