uv

2b68a3d1 - uv/tests: add and rejigger some helpers in our common test library

uv/tests: add and rejigger some helpers in our common test library This adds some variations on 'uv add' and 'uv remove' specifically for testing changes to the lock file (and not anything else). We also rejigger 'run_and_format' so that we can use it in other contexts, particularly for error reporting. And we add a 'diff_lock' helper for returning the changes made to a lock file after running a command.