feat: enforce note hash read requests to read within own contract

[LeilaWang]

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[sirasistant]

yay!

[benesjan]

@LeilaWang I am just profiling circuits and this if else makes this quite inefficient since if-elses are not real (see this comment for context).

I've noticed that we have a similar if-else here and there is a comment that the if-else will go away once we inject nonces in public kernel (#1386).

Is it the case here as well?

[LeilaWang]

Yep we won'y need the if statement here when publicly created notes have nonces! I think for now, instead of always hashing a nonce even when it's zero, which will require changing things elsewhere, we can compute the inner hash first. And only further hash the nonce to it if it's not zero:

let mut hash = compute_inner_note_hash(note);
if header.nonce != 0 {
  hash = compute_unique_hash(header.nonce, hash);
}
hash