MetricsStep<Input, Output> mixin

Adds metrics collection capability to a chain step.

Collects execution metrics like duration, success rate, error count. All metrics are stored in the chain context and can be accessed by key.

Example:

class ApiStep extends ChainStep<Request, Response>
    with MetricsStep<Request, Response> {

  static const String _metricsKey = 'api_step';

  @override
  String get metricsKey => _metricsKey;

  @override
  FutureOr<Response> executeWithMetrics(Request data, ChainContext context) {
    return apiClient.send(data);
  }
}