feat: Reuse witnesses which have been assigned constant values during ACIR gen #1074

Job	Run time
build-apple-darwin (x86_64-apple-darwin)	15m 38s
build-apple-darwin (aarch64-apple-darwin)	21m 40s
build-linux (x86_64-unknown-linux-gnu)	14m 42s
build-linux (x86_64-unknown-linux-musl)	18m 38s
	1h 10m 38s

Provide feedback