refactor: check vk hash when verifying proof

[LeilaWang]

Move VerificationKey.check_hash() to right before we call std::verify_proof_with_type(), where we pass the vk and vk hash. Eventually the hash will be checked in std::verify_proof_with_type() and check_hash can be removed.

Clean up the codebase a bit to use the same names and structs and reduce duplicated code.