Fix smart contracts not verifying proofs

[mitschabaude]

Fixes #1166
Fixes #1231

Description of the fix

Requiring a proof to verify is based on mutation of the proof value: verify() sets the shouldVerify field to Bool(true). On the other hand, the smart contract wrapper clones all input arguments to the prover to avoid modifying them (which can easily lead to bugs because we run the method multiple times). The cloning made the contract unable to mutate the original proof.

The short-term fix was to not clone proofs, similar to how we don't clone primitive provable types. It would be better if a future refactor made proof verification not dependent on mutating a method argument. Instead, we could introduce a global context which holds the proofs to potentially verify inside a circuit, and set properties on those. Also, it would be nice to have an error when we forget to verify a proof (and an explicit method to not verify them).

Changes

• adds a regression test to CI
• add a unit test checking the result of sortMethodArguments and the outputs of picklesRuleFromFunction (the latter would have caught this bug)