[CT-2923] Speed up unit test parsing by some partial parsing equivalent

[gshank]

Description

The initial unit testing branch parses the unit tests every time. In a large project with a large number of models this would probably be a performance issue.

Questions: Where should the parsed unit tests live? Should they be written out to the manifest.json or somewhere else?

Acceptance criteria

We don't need to re-read all of the yaml files in the models directory to get the unit tests.

[gshank]

Handled in #8295