Add support for Python 3.13 #2906

Compiling [macosx-shared] modules/IcePy/ValueFactoryManager.cpp
modules/IcePy/Util.cpp:619:12: error: use of undeclared identifier 'PyEval_CallObject'
  619 |     return PyEval_CallObject(type, args.get());
      |            ^
modules/IcePy/Util.cpp:654:16: error: use of undeclared identifier 'PyEval_CallObject'
  654 |         return PyEval_CallObject(type, pArgs.get());
      |                ^
2 errors generated.
make: *** [modules/IcePy/build/macosx/obj/Util.o] Error 1
make: *** Waiting for unfinished jobs....
modules/IcePy/Types.cpp:306:23: error: use of undeclared identifier 'PyEval_CallObject'
  306 |     PyObjectHandle sd{PyEval_CallObject(_slicedDataType, args.get())};
      |                       ^
modules/IcePy/Types.cpp:332:30: error: use of undeclared identifier 'PyEval_CallObject'
  332 |         PyObjectHandle slice{PyEval_CallObject(_sliceInfoType, args.get())};
      |                              ^
modules/IcePy/Types.cpp:1480:21: error: use of undeclared identifier 'PyObject_AsReadBuffer'; did you mean 'PyObject_GetBuffer'?
 1480 |                 if (PyObject_AsReadBuffer(p, &buf, &sz) == 0)
      |                     ^~~~~~~~~~~~~~~~~~~~~
      |                     PyObject_GetBuffer
/Users/joe/.local/share/mise/installs/python/latest/include/python3.13/pybuffer.h:46:17: note: 'PyObject_GetBuffer' declared here
   46 | PyAPI_FUNC(int) PyObject_GetBuffer(PyObject *obj, Py_buffer *view,
      |                 ^
modules/IcePy/Types.cpp:1480:46: error: cannot initialize a parameter of type 'Py_buffer *' with an rvalue of type 'const void **'
 1480 |                 if (PyObject_AsReadBuffer(p, &buf, &sz) == 0)
      |                                              ^~~~
/Users/joe/.local/share/mise/installs/python/latest/include/python3.13/pybuffer.h:46:62: note: passing argument to parameter 'view' here
   46 | PyAPI_FUNC(int) PyObject_GetBuffer(PyObject *obj, Py_buffer *view,
      |                                                              ^
4 errors generated.
make: *** [modules/IcePy/build/macosx/obj/Types.o] Error 1