feat: added public_witness wasm utils

[sirasistant]

Related issue(s)

Resolves #21

Description

Summary of changes

Adds get_return_witness and get_public_parameters_witness to the wasm export

Dependency additions / changes

Test additions / changes

Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.

Documentation needs

• This PR requires documentation updates when merged.

Additional context

[TomAFrench]

Can properly review and merge this next week. I don't think this fully resolves #21 though?

We can get a witness map containing the public parameters and the return values but not the public inputs (parameters + return value) without manually merging them in JS.

[sirasistant]

Added a binding for the public_witness one. I'd like to also keep the separated params/return because those are useful for aztec3 right now, but it's true that in the future we will use get_public_witness directly

[TomAFrench]

Looks good. We should add some tests for this (despite it being relatively simple logic) but we can do that in a separate PR.