Add the ability to turn on/off stats, dump them and clear them, when built with --enable-pystats #93841

This would only apply with --enable-pystats and thus #define Py_STATS. For normal builds nothing would change.

Add sys._stats_on(), sys._stats_off(), sys._stats_clear() and sys._stats_dump() functions.
This would allow us to record and dump stats for parts of a program.

This would be useful for experimentation and having stats match timings for pyperf, as we could turn on stats when starting the timer, and turn them off when stopping the timer.