feat(noir-contracts): Option<T> for get_notes

[iAmMichaelConnor]

Description

closes: #1020

Introduce Option<T> type to Noir.
Update get_notes logic:

• Remove the is_real member of some notes. Option::is_some() can now be used instead.
• Remove the is_dummy method of the NoteInterface.
• When calling the get_notes oracle, a boolean is_some is injected after the nonce to convey whether the note is a dummy or not.
• Change contract logic to unwrap Option<Note> types.

It's slightly more verbose in places, but it makes the notion of a dummy note more enshrined (and actually aligns more closely to our inital sketches of what utxo syntax might look like).

Thanks to Jake for the Option implementation!

Checklist:

• I have reviewed my diff in github, line by line.
• Every change is related to the PR description.
• I have linked this pull request to the issue(s) that it resolves.
• There are no unexpected formatting changes, superfluous debug logs, or commented-out code.
• The branch has been merged or rebased against the head of its merge target.
• I'm happy for the PR to be merged at the reviewer's next convenience.

[iAmMichaelConnor]

Having had the foresight to add a warning about unwrap_unchecked(), I then spent 45 minutes looking for why this example's e2e test was failing. It's because I was using unwrap_unchecked(). Sigh.

[iAmMichaelConnor]

Please review this one first: #1099

Edit: ok, that one's been merged. I'll rebase.

[ludamad]

LGTM although I assume for a lot of these optional note arrays they'd ideally just be dynamic arrays?

[iAmMichaelConnor]

LGTM although I assume for a lot of these optional note arrays they'd ideally just be dynamic arrays?

For the code surrounding the get_notes oracle calls, yeah we want these to eventually be dynamic. At the moment, the array lengths are hard-coded to a MAX.