Start cleanup process with setsid or nohup

If available, start the cleanup process in a new session to reduce the
likelihood of it being terminated along with the scrcpy server process
on some devices.

The binaries setsid and nohup are often available, but it is not
guaranteed.

Refs #5601 <https://github.com/Genymobile/scrcpy/issues/5601>
PR #5613 <https://github.com/Genymobile/scrcpy/pull/5613>