Async Task Queue

[vilacha]

This is a feature request without analyzing the codebase into detail but you could find it interesting anyway.

I want to suggest making the TaskQueue method async. This will allow to create some connectors that work with DDBB and Messaging systems, such RabbitMQ.

[metcoder95]

This is interesting; the change in the semantics will imply that any operation (size, push, pop) will require to handle possible async states.

The implications will often be at the performance level, and provide some limitations in the way this things are handled.

Instead of plain async/Promise, I'd prefer to change the semantic and use a callback to be passed, in that way Piscina does not need to know in advance the function type but rather just wait for the result of the expected operation.