starknet_transaction_prover: bump prover_panics_total on panic hook fire

[avi-starkware]

Bumps the new prover_panics_total counter from the panic hook before
constructing the backtrace, so dashboards can alert on panic rate without
log search. The pre-registered zero observation in install_exporter
keeps the series visible at scrape time even before the first panic.

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

[cursor]

PR Summary

Low Risk
Observability-only change to the panic hook and metrics registration; no change to proving, RPC, or abort behavior.

Overview
Adds a prover_panics_total Prometheus counter so panic rate can be alerted on from metrics, not only structured logs.

The global panic hook now increments that counter first (before backtrace capture and error! logging), so a recursive panic in those steps still records the original event. install_exporter pre-registers the series at zero like other counters so /metrics exposes it before the first panic. A unit test asserts the hook bumps the counter by one when installed.

^{Reviewed by Cursor Bugbot for commit e503ebd. 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
• starknet_transaction_prover: /health returns 503 when service is saturated #14171
• starknet_transaction_prover: bump prover_panics_total on panic hook fire #14170 👈 (View in Graphite)
• 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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