gh-140067: Fix memory leak in subinterpreter creation

The memcpy() call in _PyInterpreterState_New() was overwriting the
_malloced pointer that was set by alloc_interpreter(), causing a memory
leak when subinterpreters were destroyed.

Fixed by preserving the _malloced pointer across the memcpy().

Author: ashm-dev

Python/pystate.c

@@ -662,9 +662,14 @@ _PyInterpreterState_New(PyThreadState *tstate, PyInterpreterState **pinterp)
             status = _PyStatus_NO_MEMORY();
             goto error;
         }
+
+        void *_malloced = interp->_malloced;
+
         // Set to _PyInterpreterState_INIT.
         memcpy(interp, &initial._main_interpreter, sizeof(*interp));
 
+        interp->_malloced = _malloced;
+
         if (id < 0) {
             /* overflow or Py_Initialize() not called yet! */
             status = _PyStatus_ERR("failed to get an interpreter ID");