Function init_metrics 

pub fn init_metrics(
    cfg: &MetricsConfig,
    provider: SdkMeterProvider,
) -> Result<()>

Initialize OpenTelemetry metrics by registering the given [SdkMeterProvider] as the global meter provider.

The provider is expected to be fully configured (exporter, views, resource, etc.) by the caller before being passed in — this function only makes it globally available.

Errors

Returns an error if MetricsConfig::enabled is false.