Reworks inlining so resources are loaded lazily.

Reworks inlining so resources are loaded lazily.

Why:

* when using a hash as an input, the sources it references
  should be processed lazily instead of a whole hash being
  serialized & tokenized eagerly.

This change addresses the need by:

* See #791 - in-memory imports require such lazy processing.
  The other way, we end up with duplicated rules, and have to rely
  on advanced processing to remove them.