Deepen metric recording module

[darthfork]

Summary

• add a metric recording Module that centralizes Prometheus collector writes for webhook dedupe, async processing, repository events, and run transitions
• route webhook ingestion, async workers, push/pull_request handling, and run-transition recording through domain-level metric methods
• keep existing collector definitions, metric names, label names, and label value ordering unchanged

TDD notes

• RED: added metric recorder tests before the Module existed
• GREEN: implemented the Prometheus metric recorder with exact existing label cardinality
• REFACTOR: moved production collector mutations out of webhook/async/github/run-transition paths into the metric recorder

Cardinality guardrails

• added tests for duplicate delivery metrics, repository event metrics, run metrics, and async metrics that assert the current label sets and label ordering
• no Prometheus collector definitions in src/metrics.go were changed