fix: replace BB_ASSERT with graceful failures in verifier code paths

[AztecBot]

Summary

Converts BB_ASSERT calls in verifier code paths to graceful failures instead of panicking. When processing attacker-controlled proof data, malformed proofs should cause verification to return false (or throw a catchable exception), not crash the process via SIGABRT.

This addresses the broader hardening from the ChonkBatchVerifier security analysis — while the try/catch in batch_check already prevents crashes, these changes make the intent explicit at each verification function: invalid proofs → return false.

Changes by area

Bool-returning verification functions → return false:

• IPA (ipa.hpp): 5 assertions converted — reduce_verify_internal_native (G_zero mismatch), batch_reduce_verify (size/empty checks), reduce_verify_internal_recursive (SRS size, G_zero mismatch)
• Translator verifier: 4 PCS size-check assertions now return ReductionResult{..., false}

Non-bool functions → explicit throw_or_abort or info():

• KZG: MSM size assertion → info() warning (optional validation, non-fatal)
• Shplonk: Constructor assertion → explicit throw_or_abort (can't return from ctor)
• Shplemini: ZK consistency check → if constexpr + early return; commitment mismatch → info() warning

Deserialization/parsing → explicit throw_or_abort:

• Proof compression (proof_compression.hpp): All 11 BB_ASSERT calls in decompress_chonk_proof and helpers converted to throw_or_abort with descriptive messages
• ChonkProof (chonk_proof.cpp): from_field_elements size check converted
• Transcript (transcript.hpp): 2 bounds-check assertions in receive_from_prover and deserialize_from_buffer converted

Test plan

• chonk_tests — ProofCompressionRoundtrip + all rejection tests pass
• ultra_honk_tests — 112 pass
• commitment_schemes_tests — All IPA tests pass
• translator_vm_tests — builds successfully

ClaudeBox log: https://claudebox.work/s/6a1ba966035b66be?run=3