Test during run

[MaxHalford]

We have a --fail-fast flag to stop lea run if a view fails. This is efficient and surfaces errors as early as possible. For testing, we always run lea test after lea build. Therefore, tests that fails are always surfaced after the whole DAG succeeds.

It would cool to be able to run a test once its dependencies have been refreshed. That would surface errors as soon as possible, and save compute credits.

In terms of implementation, the difficulty is to detect when the views that a test depends on have been refreshed. In theory its straightforward, but we do have to handle the case of partial refreshes such as lea run --select git+.