fix(prover): replace .unwrap() with map_err in blob KZG verification

[chengwenxi]

Summary

• The three .unwrap() calls in BlobVerifier::verify_kzg (on KzgRsBlob::from_slice / Bytes48::from_slice) could panic the prover process if the upstream RPC returned malformed blob data, dropping every queued proof along with it.
• Convert each to .map_err(|e| anyhow!(...))? so the current request fails cleanly while the process keeps serving other proofs.
• Addresses audit finding INFO-3 from the 2026-05-15 multi-blob audit (PR feat: multi blob #935).

Test plan

• cargo check -p prover-executor-client
• Existing prover unit/integration tests pass in CI

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