[PyROOT] Use GetOptional family of C Python API where necessary

With Python 3.13, some lookup methods like `PyMapping_GetItemString` and
`PyObject_GetAttrString` became more strict. They are now always
throwing an exception in case the attribute is not found.

To make these optional lookups work again, the `GetOptional` family of
functions needs to be used.

See:
  * https://docs.python.org/3/c-api/object.html#c.PyObject_GetOptionalAttrString
  * https://docs.python.org/3/c-api/mapping.html#c.PyMapping_GetOptionalItemString

bindings/pyroot/cppyy/CPyCppyy/src/Dispatcher.cxx

@@ -484,7 +484,12 @@ bool CPyCppyy::InsertDispatcher(CPPScope* klass, PyObject* bases, PyObject* dct,
 // Python class to keep the inheritance tree intact)
     for (const auto& name : protected_names) {
          PyObject* disp_dct = PyObject_GetAttr(disp_proxy, PyStrings::gDict);
+#if PY_VERSION_HEX < 0x30d00f0
          PyObject* pyf = PyMapping_GetItemString(disp_dct, (char*)name.c_str());
+#else
+         PyObject* pyf = nullptr;
+         PyMapping_GetOptionalItemString(disp_dct, (char*)name.c_str(), &pyf);
+#endif
          if (pyf) {
              PyObject_SetAttrString((PyObject*)klass, (char*)name.c_str(), pyf);
              Py_DECREF(pyf);

bindings/tpython/src/TPyClassGenerator.cxx

@@ -87,7 +87,12 @@ TClass *TPyClassGenerator::GetClass(const char *name, Bool_t load, Bool_t silent
             std::string func_name = PyUnicode_AsUTF8(key);
 
             // figure out number of variables required
+#if PY_VERSION_HEX < 0x30d00f0
             PyObject *func_code = PyObject_GetAttrString(attr, (char *)"func_code");
+#else
+            PyObject *func_code = nullptr;
+            PyObject_GetOptionalAttrString(attr, (char *)"func_code", &func_code);
+#endif
             PyObject *var_names = func_code ? PyObject_GetAttrString(func_code, (char *)"co_varnames") : NULL;
             int nVars = var_names ? PyTuple_GET_SIZE(var_names) : 0 /* TODO: probably large number, all default? */;
             if (nVars < 0)