halo2_poseidon: Initial empty library crate #4055

Job	Run time
Bitrot check	1m 23s
Book tests	1m 19s
Code coverage	3m 26s
Build target wasm32-unknown-unknown	1m 46s
Build target wasm32-wasi	1m 33s
Intra-doc links	1m 26s
Rustfmt	14s
Test on ubuntu-latest	2m 8s
Test on i686-unknown-linux-gnu	13m 14s
Test on i686-unknown-linux-gnu with beta features	13m 19s
Test on windows-latest	1m 57s
Test on i686-unknown-linux-gnu with nightly features	15m 13s
Test on macOS-latest	1m 36s
Test on ubuntu-latest with beta features	2m 4s
Test on windows-latest with beta features	1m 56s
Test on macOS-latest with beta features	1m 36s
Test on ubuntu-latest with nightly features	2m 8s
Test on windows-latest with nightly features	2m 0s
Test on macOS-latest with nightly features	1m 39s
	1h 9m 57s

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