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/bltinmodule.c

@@ -5,6 +5,7 @@
 #include "pycore_call.h"          // _PyObject_CallNoArgs()
 #include "pycore_ceval.h"         // _PyEval_Vector()
 #include "pycore_compile.h"       // _PyAST_Compile()
+#include "pycore_fileutils.h"     // _PyFile_Flush
 #include "pycore_long.h"          // _PyLong_CompactValue
 #include "pycore_modsupport.h"    // _PyArg_NoKwnames()
 #include "pycore_object.h"        // _Py_AddToAllObjects()