Implement error codes for the `mtree_verify` instructions.

[Fumuran]

This PR implements the ability to specify error codes for mtree_verify instruction the same way it is done for assert instructions.

Related issue: #1264

[Fumuran]

I noticed that for some reason we still use Felt as an error code for the U32assert2 operation (link), so I probably should create an issue to change it to the u32.

[bobbinth]

We should put this on hold until #1277 is merged and then make this work with the new structure.

[bitwalker]

@Overcastan I think you'll find it pretty easy to port this to #1277, if you look at how your implementation of u32clz, etc. was ported to the new structure, it's basically identical, though you'll probably want to reference the Assert non-terminal production in assembly/src/parser/grammar.lalrpop to see how to handle error code immediates specifically. Other than that, most everything else is relatively unchanged from the implementation in this PR.

[plafer]

@Overcastan Are you still working on this?

[bobbinth]

Now that #1277 has been merged, we should refresh this PR.

[Fumuran]

@plafer Yep, I'll rework it to work with a new version of assembler.

[Fumuran]

I decided to create a new PR for this issue, I think it will be easier than resolving conflicts in this one.