Start cleanup process with setsid()

Reimplement c59a3c3169973abb4ce236e06990d58ae6567481 using Os.setsid().

Refs #5613 comment <https://github.com/Genymobile/scrcpy/pull/5613#issuecomment-2527045669>

Suggested-by: Simon Chan <1330321+yume-chan@users.noreply.github.com>