Start a recorder when the next race begins instead of driving the menus

What to know

Driving a game's menus from a script is slow and fragile, and in a shared emulator it can collide with another session. When the game has a state variable that marks the start of a run, a small watcher can wait for it and start the recorder at that moment, whoever starts the run.

POD's race phase DAT_005920a4 is 2 during the countdown. run/vm/racewait.sh polls it twice a second through /proc/PID/mem (finding the PID again each time, since the game may restart) and then runs the recorder. It caught two races from their countdown, one started by another session. GameFrame's recorder does the same: memrec.py record SPEC --name GAME.EXE --wait 0x5920a4=2.

Limits:

• Polling misses the first moments. At 0.5 s on a slow VM, POD's recordings start at countdown "5" or "4". Poll faster, or trigger on an earlier state, if the start matters.
• Under sudo, write the output to a new file: /tmp files owned by another user cannot be written even by root when fs.protected_regular is set (Debian's default).