Short test suite

Currently, the full `pytest` test suite takes about 30 minutes to run, and some require the GCS credentials. This is useful as an automated action for a PR, but is time-consuming between commits to run locally. It would be nice to write a separate set of fast unit tests that don't require secrets, or to tag the short tests that don't require secrets so that they can be run separately from the long tests

Start by running the current pytest suite and identify which tests take most of the roughly 30 minutes or require GCS credentials. Review the existing test organization and pytest configuration, then separate or tag the credential-free short tests. Done means a clearly documented command runs the fast tests locally without secrets while the full suite remains available for PR automation.

Written by the indexing model from the issue text.