Closes#140. In restart_daemon, the old process's stdout pipe was never
explicitly closed after p.wait() returned, leaking the fd until the
supervisor object was GC'd. Similarly, when the watch loop converged
(all children dead), no pipe was closed. Both paths now call
p.stdout.close() immediately after the process is confirmed exited.
Tests enforce this with warnings.simplefilter("error", ResourceWarning)
in TestSupervisor.setUp.
didericis-claude