starknet_transaction_prover: origin-level breadcrumbs for validation errors

[avi-starkware]

Splits validation-error logging so each origin (request body, RPC,
proving) carries an event tag and trimmed payload context, making it
straightforward to root-cause production failures from the structured
log stream. Also adds an in-test microbenchmark for HttpMetricsLayer
overhead so any regression in the hot path is visible.

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com

[cursor]

PR Summary

Low Risk
Observability-only logging and test-only benchmarks; no change to proving logic, auth, or transaction handling.

Overview
Adds structured validation and failure logging in the proving path so production issues can be filtered by stable event / reason fields without logging transaction calldata.

In virtual_snos_prover, each validation failure now emits a warn with event = "validation_error" and a specific reason (pending block, non-invoke tx, invalid input) via inspect_err on extract/validate. The RPC layer’s prove handler logs failures with event = "prove_transaction_failed" and outcome aligned with prover_prove_transaction_outcome_total metrics.

Also introduces ignored release microbenchmarks (server/overhead_bench) to compare baseline Tower throughput vs HttpMetricsLayer steady-state overhead for observability rollout checks.

^{Reviewed by Cursor Bugbot for commit b7d03bd. Bugbot is set up for automated code reviews on this repo. Configure here.}

[avi-starkware]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• starknet_transaction_prover: origin-level breadcrumbs for validation errors #14172 👈 (View in Graphite)
• starknet_transaction_prover: /health returns 503 when service is saturated #14171
• starknet_transaction_prover: bump prover_panics_total on panic hook fire #14170
• starknet_transaction_prover: HTTP request count + latency + in-flight metrics #14169
• starknet_transaction_prover: proving-job duration + outcome metrics #14168
• starknet_transaction_prover: Prometheus /metrics endpoint with build_info #14167
• starknet_transaction_prover: global panic hook + graceful SIGTERM shutdown #14166
• starknet_transaction_prover: per-request structured log with request-id #14165
• starknet_transaction_prover: redact URL credentials in logs and add startup banner #14164
• starknet_transaction_prover: add /health endpoint via HealthLayer #14163
• starknet_transaction_prover: add --log-format text|json CLI flag #14162
• main

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[reviewable-StarkWare]

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