Add unit tests for local container launch functions in `xm_local.execution`.
Add unit tests for local container launch functions in `xm_local.execution`.

PiperOrigin-RevId: 465510302
Change-Id: I7a8f34fab7c050ceb67817b497ce50ee518d904f
GitOrigin-RevId: 425a051db3c71a7b4b02dab5ee416fd9e2df7e54

deepmind/xmanager,deepmind/xmanager