Review code executed at import time

[lbianchi-lbl]

It would be useful to do a review or what code is executed when importing a particular module across the complete codebase.

Generally, we'd probably want to keep import-level code as minimal as possible; otherwise, the chance of introducing unexpected behavior or bugs that are difficult to detect will be higher.

[lbianchi-lbl]

This is related to #1013, in that making sure that any given module can be imported "cleanly" requires some way of gracefully handling unavailable modules imported there.