GH-131238: More refactoring of core header files (GH-131351)

Adds new pycore_stats.h header file to help break dependencies involving the pycore_code.h header.

Python/bytecodes.c

@@ -29,6 +29,7 @@
 #include "pycore_long.h"          // _PyLong_ExactDealloc()
 #include "pycore_setobject.h"     // _PySet_NextEntry()
 #include "pycore_sliceobject.h"   // _PyBuildSlice_ConsumeRefs
+#include "pycore_stackref.h"
 #include "pycore_tuple.h"         // _PyTuple_ITEMS()
 #include "pycore_typeobject.h"    // _PySuper_Lookup()