Support verification of multiple circuit proofs

[noam-starkware]

Note

Medium Risk
Changes the circuit-verifier API and core verification flow to iterate over multiple proofs, which could affect soundness/correctness if vector alignment or shared-context assumptions are wrong.

Overview
Extends verify_circuit / build_verification_circuit to accept vectors of CircuitConfig, Proof, and CircuitPublicData, and verifies them sequentially in a single Context via a new verify_circuit_single_proof helper.

Updates recursion-related tests to use the new multi-proof API and adds a privacy test that verifies a 2-to-1 recursion scenario by proving twice and verifying both proofs together, with basic consistency checks (e.g., shared pcs_config).

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