A GenServer that keeps track of user pids of temporary directories.

Temporary directories are created via calls to Antikythera.Tmpdir.make/2. This GenServer communicates with the caller process and monitors its death to make sure that the directories are eventually deleted.

Currently we do not impose upper limit on volume and I/O usage since number of concurrently running processes is capped by executor pools. As a result we also skip checking association of "executor pool" and "calling code (gear)".