fix(verify): Only verify halo2 proofs once per transaction

[teor2345]

Motivation

There is only one aggregated halo2 proof per transaction, but Zebra is verifying the same proof for each action.

This uses a lot of RAM and CPU, and stops Zebra syncing to the tip.

Solution

Only verify the halo2 proof once per transaction.

Review

This bug is blocking almost all other work, it's urgent.

Reviewer Checklist

• All Halo2 proofs and Orchard Actions are being verified
• CI passes
• Full sync passes

[teor2345]

I'm running a full sync here:
https://github.com/ZcashFoundation/zebra/actions/runs/2618944705

It should finish in around 6 hours.

[oxarbitrage]

Definitely good, no need to do this inside the loop. Nice find.

[oxarbitrage]

It should finish in around 6 hours.

It seems this should be merged anyway even if it does not make the difference in time right now, it is a performance fix.

[upbqdn]

That's a great find!

[codecov]

Codecov Report

Merging #4752 (63e0877) into main (42ef884) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #4752      +/-   ##
==========================================
- Coverage   78.87%   78.86%   -0.02%     
==========================================
  Files         306      306              
  Lines       37557    37545      -12     
==========================================
- Hits        29624    29608      -16     
- Misses       7933     7937       +4     

[upbqdn]

All looks good.

[dconnolly]

Double-checked the spec and the existing Halo2 verifier service, looks good!

When we push a new halo2::Item to the batch verifier, it produces orchard::circuit::Instances from each Action in the transacton, and then the whole set of Instances is passed as input to verify() a single Halo2 aggregate proof, so this change is correct.

[gustavovalverde]

Admin merged, as the full sync got stuck and we need the fix anyways.