feat: FlowControl: add FromStr impl #334

Job	Run time
cargo-deny (advisories)	17s
lint	16s
cargo-deny (bans licenses sources)	17s
aarch64-apple-darwin / build	42s
aarch64-apple-ios / build	46s
aarch64-unknown-linux-gnu / build	23s
aarch64-unknown-linux-musl / build	51s
arm-linux-androideabi / build	36s
armv7-linux-androideabi / build	38s
i686-pc-windows-gnu / build	1m 35s
i686-pc-windows-msvc / build	1m 57s
i686-unknown-linux-gnu / build	29s
msrv-aarch64-apple-darwin / build	40s
i686-unknown-linux-musl / build	1m 2s
msrv-arm-linux-androideabi / build	37s
msrv-x86_64-pc-windows-msvc / build	55s
msrv-x86_64-unknown-freebsd / build	41s
msrv-x86_64-unknown-linux-gnu / build	48s
msrv-x86_64-unknown-linux-musl / build	54s
msrv-x86_64-unknown-netbsd / build	45s
x86_64-apple-darwin / build	54s
x86_64-pc-windows-gnu / build	3m 51s
x86_64-pc-windows-msvc / build	2m 12s
x86_64-unknown-freebsd / build	23s
x86_64-unknown-linux-musl / build	1m 1s
x86_64-unknown-linux-gnu / build	47s
x86_64-unknown-netbsd / build	36s
	24m 53s

Provide feedback