fix(bb-prover): replace a dead pooled bb verifier (port aztec-labs-eng/aztec-node#354 to v6)

[charlielye]

Ports aztec-labs-eng/aztec-node#354 to v6 as a labs patch, labs-patches/0011-….

#354 fixes the RPC proof verifier's pool. When a pooled bb died, the pool kept handing out the dead handle for the life of the node, and verifyProof reported the failure as { valid: false }, so valid transactions were rejected as having invalid proofs until restart. With the fix:

• A pooled instance replaces its own bb process when it dies, using bb.js's respawn.
• A verification whose bb died or could not start is retried once, then fails as ProofVerifierUnavailableError instead of as an invalid proof.
• The pool is a queue of slots, each starting its bb on first use.

The bb.js half it relies on, #25548, is already on v6 via the rolling port in #25565. v6 builds labs against its own bb.js, so no pin change is needed.

How

labs stays at a0d73c0aed. #354's squash commit (aztec-labs-eng/aztec-node@8556dfb6a6) is cherry-picked onto the existing series and exported, with no conflicts. The existing patches 0001 and 0010 are unchanged; the new one is numbered 0011 so it sorts after them.

The patch drops out at the next labs bump past aztec-node main at 8556dfb6a6.

Verification

• ./labs-patches/bootstrap.sh check: the series applies cleanly to the gitlink.
• The patch matches fix(noir): use latest compiler to pass array to oracle function #354's merged diff: 10 files, +472/−94.
• fix(noir): use latest compiler to pass array to oracle function #354's tests ran green in aztec-node CI. They run against v6 in this PR's CI.

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