[Host] Refactor 'Retry' delegate in IConsumerErrorHandler as response type

[EtherZa]

While the discussed 'pipeline reimagination' was a little too ambitious for the time that I have available; I have refactored the implementation to extract the retry delegate from IConsumerErrorHandler.OnHandleError and to rather include it as a response value. This does introduce a breaking change, but allows the handler to perform all of the previous logic albeit with a small change for retry.

The OnHandlerError method signature therefore changes from:

Task<ConsumerErrorHandlerResult> OnHandleError(T message, Func<Task<object>> retry, IConsumerContext consumerContext, Exception exception);

to:

// where `attempts` is the execution count
Task<ConsumerErrorHandlerResult> OnHandleError(T message, IConsumerContext consumerContext, Exception exception, int attempts);

In order to retry the execution (with a new scope as requried), the implemented method must return ConsumerErrorHandlerResult.Retry. Further to this, abstract implmentations of IConsumerErrorHandler have been added with methods to support Failure(), Success(object? response = null) and Retry() for a cleaner experience (similar to return Ok(); with asp.net controllers).

Example:

public class RetryHandler<T> : ConsumerErrorHandler<T>
{
    private static readonly Random _random = new();

    public override async Task<ConsumerErrorHandlerResult> OnHandleError(T message, IConsumerContext consumerContext, Exception exception, int attempts)
    {
        if (attempts <= 3)
        {
            var delay = (attempts * 1000) + (_random.Next(1000) - 500);

            await Task.Delay(delay, consumerContext.CancellationToken);
            return Retry();
        }

        return Failure();
    }
}

[zarusz]

This is an excellent and pragmatic approach to improving the error-handling pipeline while achieving the message scope recreation as discussed in issue #347. The implementation is mostly backward-compatible and could potentially outperform the Func<Task> next delegate approach.

I've suggested a few minor adjustments to the documentation for clarity and completeness.

Once those are addressed, I’ll be happy to approve the PR. Great work!

[zarusz]

It's been released under v3 rc:
https://www.nuget.org/packages/SlimMessageBus.Host.AzureServiceBus/3.0.0-rc901