[Feature]: Emit events when a task retries

[thalesraymond]

Description

Currently, the RetryingExecutionStrategy handles retries silently. The main TaskRunner only emits taskStart and taskEnd. Users have no visibility into whether a task is succeeding on the first try or failing and retrying, which is crucial for debugging flaky services.

Proposed Solution

1. Add a taskRetry event to RunnerEventPayloads in RunnerEvents.ts.

     taskRetry: {
       step: TaskStep<TContext>;
       attempt: number;
       error: any;
     };

2. Update RetryingExecutionStrategy so it accepts the EventBus (or a callback) to emit this event when a retry is triggered.

Alternatives Considered

Passing a custom logger to the strategy, but an event-driven approach is more consistent with the rest of the library.