starknet_transaction_prover: per-request structured log with request-id

[avi-starkware]

Adds RequestLogLayer that emits one event="http_request" log line per
request with request_id, method, path, status, and latency_ms. The id is
accepted from x-request-id or generated as a 128-bit random hex string,
and is echoed back on the response so callers can quote it. No request
body bytes are inspected (transaction calldata is private user data).

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

[cursor]

PR Summary

Medium Risk
Changes the privacy-pool gateway HTTP stack and request-id handling at the OHTTP envelope boundary; behavior is mostly observability but incorrect correlation could weaken unlinkability.

Overview
Adds RequestLogLayer as the outermost HTTP middleware on both plain HTTP and HTTPS JSON-RPC servers in starknet_transaction_prover, so each request gets one structured event="http_request" log line with request_id, method, path (truncated for logging only), status, and latency_ms.

The layer accepts a safe client x-request-id (length-capped, printable ASCII) or generates a UUID v4, forwards the id on the request, echoes it on the response, and does not attach that envelope id to downstream tracing spans—documented so OHTTP relay-visible ids are not joinable with decapsulated inner traffic. Request bodies are never read.

^{Reviewed by Cursor Bugbot for commit 49a7855. Bugbot is set up for automated code reviews on this repo. Configure here.}

[reviewable-StarkWare]

This change is 

[avi-starkware]

• starknet_transaction_prover: document observability surface in README #14203
• starknet_transaction_prover: origin-level breadcrumbs for validation errors #14172
• 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,tower_ohttp: OHTTP-unlinkable request-id for decapsulated content #14222
• starknet_transaction_prover: per-request structured log with request-id #14165 👈 (View in Graphite)
• 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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