Notify reviewers how long unit tests took to run

[Patater]

Is your feature request related to a problem? Please describe. Sometimes we might accidentally add unit tests that run too slowly (e.g. when they forget to mock the network or filesystem).

Describe the solution you'd like It would be cool if our CI posted a comment about unit test run-time, so we could have our "code review" attention pulled to this sort of issue in the future. We are aiming for less than 10 seconds to run all unit tests. There are pytest plugins which will report that kind of thing.

Describe alternatives you've considered Rather than burden reviewers with more things to look at, we could have PRs fail testing if unit tests take longer than 10 seconds to run.