halo2_poseidon: Initial empty library crate #4056

Job	Run time
Bitrot check	1m 24s
Book tests	1m 21s
Test on ubuntu-latest	1m 39s
Test on i686-unknown-linux-gnu	13m 9s
Test on windows-latest	1m 44s
Test on i686-unknown-linux-gnu with beta features	13m 3s
Test on macOS-latest	1s
Test on ubuntu-latest with beta features	1m 39s
Test on windows-latest with beta features	1m 42s
Test on i686-unknown-linux-gnu with nightly features	14m 59s
Test on macOS-latest with beta features	1m 32s
Test on ubuntu-latest with nightly features	1m 42s
Code coverage	3m 26s
Build target wasm32-unknown-unknown	1m 45s
Test on windows-latest with nightly features	1m 46s
Build target wasm32-wasi	1m 34s
Intra-doc links	1m 27s
Test on macOS-latest with nightly features	1m 36s
Rustfmt	15s
	1h 5m 44s

Provide feedback