add halo2_gadgets_optimized #266

Job	Run time
Test on ubuntu-latest	10m 50s
Test on windows-latest	14m 31s
Test on i686-unknown-linux-gnu	22m 53s
Test on macOS-latest	18m 27s
Test on i686-unknown-linux-gnu with beta features	22m 25s
Test on ubuntu-latest with beta features	10m 38s
Test on i686-unknown-linux-gnu with nightly features	26m 8s
Test on windows-latest with beta features	14m 1s
Test on macOS-latest with beta features	17m 31s
Bitrot check	1m 55s
Test on ubuntu-latest with nightly features	13m 3s
Book tests	1m 19s
Test on windows-latest with nightly features	16m 50s
Test on macOS-latest with nightly features	12m 43s
Build target wasm32-unknown-unknown	1m 55s
Code coverage	21m 34s
Build target wasm32-wasi	1m 38s
Intra-doc links	1m 25s
Rustfmt	17s
	3h 50m 3s

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