code: func WithMetricsCollector(ctx context.Context) (context.Context, *MetricsCollector) {
  	metricsCollector := &MetricsCollector{metrics: &InvocationMetrics{}}
  	ctxWithMetrics := context.WithValue(ctx, metricsCollectorID{}, metricsCollector)
  	return ctxWithMetrics, metricsCollector
  }
docs: // WithMetricsCollector provides a new context with the a MetricsCollector that records performance metrics for invocations