halo2_poseidon: Add no-std support #4076

Job	Run time
Book tests	1m 24s
Intra-doc links	1m 35s
Bitrot check	1m 25s
Code coverage	3m 28s
Test on ubuntu-latest	2m 53s
Test on i686-unknown-linux-gnu	3m 8s
Test on windows-latest	6m 28s
Test on i686-unknown-linux-gnu with beta features	3m 5s
Test on macOS-latest	2m 40s
Test on i686-unknown-linux-gnu with nightly features	3m 11s
Rustfmt	13s
Test on ubuntu-latest with beta features	2m 52s
Test on windows-latest with beta features	6m 36s
Build target wasm32-unknown-unknown	1m 52s
Test on macOS-latest with beta features	2m 36s
Build target wasm32-wasi	1m 41s
Test on ubuntu-latest with nightly features	2m 51s
Test on windows-latest with nightly features	5m 48s
Test on macOS-latest with nightly features	2m 50s
	56m 36s

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