gh-128679: Redesign tracemalloc locking (#128888)

* Use TABLES_LOCK() to protect 'tracemalloc_config.tracing'.
* Hold TABLES_LOCK() longer while accessing tables.
* tracemalloc_realloc() and tracemalloc_free() no longer
  remove the trace on reentrant call.
* _PyTraceMalloc_Stop() unregisters _PyTraceMalloc_TraceRef().
* _PyTraceMalloc_GetTraces() sets the reentrant flag.
* tracemalloc_clear_traces_unlocked() sets the reentrant flag.