Rework (or remove?) merkle module to avoid unwraps

[phated]

Problem

The merkle.rs module in this crate uses a ton of unwraps. As soon as we land #151, we'll be able to avoid these.

Proposed solution

Either rewrite the module or remove it if we can. I'm not clear on where the merkle stuff should be happening (acvm vs backend).

Alternatives considered

No response

Additional context

No response

Submission Checklist

• Once I hit submit, I will assign this issue to the Project Board with the appropriate tags.

[TomAFrench]

I'm in favour of removing the merkle tree implementation entirely. The compute_merkle_root function should live down in ACVM to match the other black box functions. Alternatively we remove this black box function entirely as we can implement it in a library while being more flexible

The merkle tree implementation is only used for calculating inputs for test cases so we can then remove it entirely.

[TomAFrench]

We can also remove unwraps if we get a rust pedersen implementation afaik as we only throw errors due to potential wasm issues I think.

[TomAFrench]

Closing as this code is being deleted in #205