Populate recursive components asynchronously

[bakape]

• If recordReference is not in the cache on query, schedule it to be fetched in a separate goroutine to not block retrieving any subsequent components.
• Add Await() error method to component interface, that blocks until a component is retrieved.
  • Block only for async recordReference retrieval.

Having a separate Await() method instead of returning errors on read allows for error to be propagated before the first write to destination.

[bakape]

This will not only make the order of error propagation non-deterministic, but also introduce a need for an extra runtime component and complicate #8, making it require a growing thread pool to implement this. Also, this optimization would mostly benefit miss-often caches rather than caches that are mostly hit.