Feature/add v2 txm metrics

[cawthorne]

Add v2 TXM Metrics with Per-Account Tracking

Metric can be seen for Starknet Testnet nodes at the endpoint:
http://10.13.80.235:6688/plugins/starknet.SN_SEPOLIA/metrics
(Pod IP may rotate).

infra-k8s preview-stage PR is here:
https://github.com/smartcontractkit/infra-k8s/pull/32851/files

ArgoCD Staging is here:
https://argo.main.stage.cldev.sh/applications/cl-ocr-starknet-testnet?view=tree&resource=
https://argo.main.stage.cldev.sh/applications/cl-ocr-starknet-testnet?view=list&resource=&node=%2FPod%2Fchainlink%2Fcl-ocr-starknet-testnet-0-67b97d78b5-pkkg5%2F0

Summary

Implements comprehensive transaction manager metrics following Chainlink-EVM patterns, with per-account granularity and dual telemetry support (Prometheus + OpenTelemetry/Beholder).

Metrics

All metrics are labeled by chainID and accountAddress for per-account monitoring:

• txm_num_broadcasted_transactions: Counter for successful transaction broadcasts
• txm_num_confirmed_transactions: Counter for confirmed transactions (handles re-orgs)
• txm_num_nonce_gaps: Counter for nonce gap events requiring resync
• txm_nonce_rebroadcast: Counter for nonce rebroadcasts (indicates resync frequency)
• txm_time_until_tx_confirmed: Histogram of confirmation durations
• txm_enqueue_failed: Counter for enqueue failures (queue full)
• txm_next_nonce: Gauge for current next nonce per account

Implementation

• Dual telemetry: Prometheus (via promauto) and OpenTelemetry/Beholder metrics recorded in parallel
• Thread-safe: Uses sync.Once for safe metric initialization
• Per-account tracking: All metrics labeled with both chainID and accountAddress
• Nonce-based tracking: Internal transaction tracking uses nonce instead of hash for reliability

Files Changed

• relayer/pkg/chainlink/txm/txm.go - Metric integration with per-account tracking
• relayer/pkg/chainlink/txm/txm_metrics.go - Prometheus and Beholder metrics implementation
• relayer/pkg/chainlink/txm/txstore.go - Nonce-based transaction tracking
• Test files - Comprehensive test coverage

[toblich]

I lack a lot of context here, but as far as I can tell it LGTM

[cl-sonarqube-production]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube