gh-131253: free-threaded build support for pystats (gh-137189)

Allow the --enable-pystats build option to be used with free-threading.  The
stats are now stored on a per-interpreter basis, rather than process global.
For free-threaded builds, the stats structure is allocated per-thread and
then periodically merged into the per-interpreter stats structure (on thread
exit or when the reporting function is called). Most of the pystats related
code has be moved into the file Python/pystats.c.

Python/lock.c

@@ -6,6 +6,7 @@
 #include "pycore_parking_lot.h"
 #include "pycore_semaphore.h"
 #include "pycore_time.h"          // _PyTime_Add()
+#include "pycore_stats.h"         // FT_STAT_MUTEX_SLEEP_INC()
 
 #ifdef MS_WINDOWS
 #  ifndef WIN32_LEAN_AND_MEAN
@@ -62,6 +63,8 @@ _PyMutex_LockTimed(PyMutex *m, PyTime_t timeout, _PyLockFlags flags)
         return PY_LOCK_FAILURE;
     }
 
+    FT_STAT_MUTEX_SLEEP_INC();
+
     PyTime_t now;
     // silently ignore error: cannot report error to the caller
     (void)PyTime_MonotonicRaw(&now);