Support async syntax and operations

[mostafa]

The basic event loop support was added to k6 since v0.37.0, and ever since, it has been improved and also implemented in some extensions. Kafka-go library also supports async operations on Reader and Writer, as mentioned in the README in some sections:

The Reader description:

A Reader ..., and exposes an API that supports asynchronous cancellations and timeouts using Go contexts.

The Writer features:

• Synchronous or asynchronous writes of messages to Kafka.
• Asynchronous cancellation using contexts.

So, it is safe to say that supporting it would be a nice-to-have feature.