halo2_poseidon: Add no-std support #4078

Job	Run time
Bitrot check	1m 24s
Book tests	1m 25s
Build target wasm32-unknown-unknown	1m 50s
Build target wasm32-wasi	1m 37s
Intra-doc links	1m 28s
Rustfmt	15s
Test on ubuntu-latest	7m 17s
Test on windows-latest	9m 59s
Test on i686-unknown-linux-gnu	13m 33s
Test on macOS-latest	6m 31s
Test on i686-unknown-linux-gnu with beta features	13m 37s
Test on ubuntu-latest with beta features	7m 25s
Test on i686-unknown-linux-gnu with nightly features	16m 0s
Test on windows-latest with beta features	11m 18s
Test on macOS-latest with beta features	6m 47s
Code coverage	3m 42s
Test on ubuntu-latest with nightly features	8m 11s
Test on windows-latest with nightly features	12m 8s
Test on macOS-latest with nightly features	7m 10s
	2h 11m 37s

Provide feedback