Upgrade to ark-* 0.5.0

[hrxi]

This allows us to drop our local patches. :)

[paberr]

You removed ToBeBytesGadget, did we not use that?
Apart from that, LGTM

Regarding the current check failures:

• The failing web-client looks a bit like the loop unrolling problem if I'm not mistaken, but it should be fixed in 0.5 through a conditional compilation flag.
• The tests fail in the check whether we have enough signers. I already looked into it but couldn't find an obvious issue.

[paberr]

Also, while reviewing the failing tests, I stumbled across the following code from Bruno (check_signers function):

        // num_signers >= min_signers
        num_signers.is_cmp(&min_signers, Ordering::Greater, true)

It looks to me that there's a mismatch between the comment and the code.
We should ensure consistency between the circuit code and our regular consensus condition though. If the consensus accepts blocks with num_signers == min_signers but the ZKP does not, we can run into an issue where we can not create ZKPs anymore.

[paberr]

Also, we need to check that the upgrade did not modify any constraints that invalidate our generated ZKP keys.

[hrxi]

There's also this issue I created wrt. the test failure: arkworks-rs/r1cs-std#151. We can probably just copy that function to our codebase without the panic.

You removed ToBeBytesGadget, did we not use that?

This feature was added by 0.5.0 with the same name and same functionality, so I could just remove our ToBeBytesGadget.

• The failing web-client looks a bit like the loop unrolling problem if I'm not mistaken, but it should be fixed in 0.5 through a conditional compilation flag.

Yup on both, but maybe another loop unrolling problem appeared since then. I'll look into it.

We should ensure consistency between the circuit code and our regular consensus condition though. If the consensus accepts blocks with num_signers == min_signers but the ZKP does not, we can run into an issue where we can not create ZKPs anymore.

Does that mean we need to adjust the consensus code because we can't adjust the ZKP code anymore?