feat: NMv3: Prometheus metrics for network monitor

[jstuczyn]

NYM-754

Wires up a /v1/metrics/prometheus scrape endpoint for the v3 orchestrator, along with the metric variants it exposes and the call-site instrumentation that feeds them. The handle follows the existing nym-node wrapper pattern: a singleton PROMETHEUS_METRICS backed by nym_metrics, with every variant pre-registered at startup so scrapes never see a missing series.

Summary

• Request lifecycle counters — port requests, agent announce (good / bad / duplicate / contract success / failure), testrun requests (total / unknown-agent / unannounced / empty / non-empty / result submissions / errors), eviction counts.
• Timing histograms — test duration (seconds), approximate node latency (ms), avg test packet RTT (ms), received packets ratio, node refresh cycle duration (seconds).
• Topology gauges — bonded nodes broken out by NodeType (mixnode / gateway / mixnode_and_gateway / unknown), plus successful / failed self-described retrievals.
• Liveness gauges — in-flight testruns (testrun_in_progress row count), total / announced known agents.
• Volume counters — total test packets sent / received across all submitted testruns.

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Project	Deployment	Actions	Updated (UTC)
nym-explorer-v2	Ready	Preview, Comment	Apr 24, 2026 9:38am

2 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
docs-nextra	Ignored	Preview	Apr 24, 2026 9:38am
nym-node-status	Ignored	Preview	Apr 24, 2026 9:38am