Missing ETUI interaction for pull from registry (registry source only)

Today when pulling from the docker daemon there is a ETUI interaction showing intermediate progress. There is no equivalent for the pull status from a `registry:` source. An addition is needed in stereoscope to pre-fetch the image instead of a just-in-time fetch at parse, as done today.

Start by reading stereoscope's handling of the `registry:` source and compare it with the existing docker-daemon pull path that shows intermediate ETUI progress. Trace where registry images are currently fetched during parsing. Done means registry pulls are prefetched and expose equivalent ETUI interaction and progress before parsing.

Written by the indexing model from the issue text.