Add a test to check for leftover pipeline artifacts

[jayson-lennon]

The test needs to run after all testing is complete, so putting it into the justfile seems appropriate. It just needs to check for any files in the temporary directory (/tmp on Linux, IDK for Windows/Mac) that match the prefix in the code.

Once the test is added, a comment should be placed in the test and in the code to keep the tempfile prefix in sync.