MetricsConfigLoader

Loads the Prometheus metrics backend from llm4s.metrics: a org.llm4s.metrics.MetricsCollector, plus the org.llm4s.metrics.PrometheusEndpoint serving it when one was started.

This replaces Llm4sConfig.metrics(), which left core with Prometheus (#1133): MetricsConfigLoader.default() is the same call against the same keys.

Configuration keys, with their defaults in this module's reference.conf:

• llm4s.metrics.enabled: enable metrics collection (default: false)
• llm4s.metrics.prometheus.enabled: use the Prometheus backend when metrics are enabled (default: true)
• llm4s.metrics.prometheus.port: port for the /metrics HTTP endpoint (default: 9090)

Example application.conf:

llm4s {
 metrics {
   enabled = true
   prometheus {
     enabled = true
     port = 9090
   }
 }
}

When enabled, loading starts the HTTP endpoint; stop it with PrometheusEndpoint.stop(). Other code should receive the MetricsCollector by dependency injection rather than read these keys itself.