add CI check for unused imports in Cargo

[veljkovranic]

We had a ton of unused dependencies, this PR is adding a check for them and removing all the unused ones.

cargo-machete found the following unused dependencies in this directory:
poseidon2 -- ./poseidon2/Cargo.toml:
Done!
	hex
provekit-bench -- ./tooling/provekit-bench/Cargo.toml:
	ark-ff
	ark-std
	noir_artifact_cli
	noirc_abi
	noirc_artifacts
	rand
	whir
provekit-cli -- ./tooling/cli/Cargo.toml:
	serde
provekit-ffi -- ./tooling/provekit-ffi/Cargo.toml:
	acir
	noirc_abi
provekit-common -- ./provekit/common/Cargo.toml:
	rand
	rand08
	zeroize
provekit-r1cs-compiler -- ./provekit/r1cs-compiler/Cargo.toml:
	ark-crypto-primitives
provekit-prover -- ./provekit/prover/Cargo.toml:
	ark-crypto-primitives
	rand
	rayon
	skyscraper
	spongefish
	spongefish-pow