feat(abi)!: merge both abi encoding/decoding methods

[TomAFrench]

Related issue(s)

Resolves #851 (comment)

Description

Summary of changes

We've switched to tracking public inputs in the evaluator in BTreeSet rather than a Vec which naturally deduplicates them, this allows us to:

• stop deduplicating these inputs manually up in the Nargo CLI.
• always encode to a WitnessMap for both proving and verifying (before flattening this into an naturally deduped array for verification but we can remove this as well if the backends take a WitnessMap for verifier inputs)

The only sad thing about this PR is it brings back the boolean flag in the abi encoding functions (but we'll be able to handle this better with #678)

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.
• This PR requires documentation updates when merged.

Additional context

[kevaundray]

LGTM -- pending merge conflicts