gh-41137: Refactor reference counting to use _Py_REFCNT and Py_SET_REFCNT
    
This change replaces direct access to ob_refcnt with proper API
functions:
- Use _Py_REFCNT() for reading reference counts
- Use Py_SET_REFCNT() for setting reference counts

This ensures compatibility with Python's free-threaded mode and follows
Python's recommended practices for reference count manipulation.



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### ⌛ Dependencies

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URL: #41137
Reported by: Chenxin Zhong
Reviewer(s): Tobias Diez

Author: Release Manager

src/sage/matrix/args.pxd

@@ -1,4 +1,5 @@
 from cpython.object cimport PyObject
+from cpython.ref cimport _Py_REFCNT
 from sage.structure.element cimport Element, Matrix
 from sage.structure.parent cimport Parent
 
@@ -64,7 +65,7 @@ cdef class MatrixArgs:
         Can we safely return self.entries without making a copy?
         A refcount of 1 means that self.entries is the only reference.
         """
-        return (<PyObject*>self.entries).ob_refcnt == 1
+        return _Py_REFCNT(<PyObject*>self.entries) == 1
 
     cdef inline bint need_to_convert(self, x) noexcept:
         """Is ``x`` not an element of ``self.base``?"""

src/sage/rings/integer.pyx

@@ -207,6 +207,9 @@ new_gen_from_integer = None
 cdef extern from *:
     int unlikely(int) nogil  # Defined by Cython
 
+cdef extern from "Python.h":
+    void Py_SET_REFCNT(PyObject*, Py_ssize_t) nogil
+
 cdef object numpy_long_interface = {'typestr': '=i4' if sizeof(long) == 4 else '=i8'}
 cdef object numpy_int64_interface = {'typestr': '=i8'}
 cdef object numpy_object_interface = {'typestr': '|O'}
@@ -7724,7 +7727,7 @@ cdef PyObject* fast_tp_new(type t, args, kwds) except NULL:
     # Objects from the pool have reference count zero, so this
     # needs to be set in this case.
 
-    new.ob_refcnt = 1
+    Py_SET_REFCNT(<PyObject*>new, 1)
 
     return new
 

src/sage/rings/real_double.pyx

@@ -45,6 +45,9 @@ from libc.string cimport memcpy
 from cpython.object cimport *
 from cpython.float cimport *
 
+cdef extern from "Python.h":
+    void Py_SET_REFCNT(PyObject*, Py_ssize_t) nogil
+
 from sage.ext.stdsage cimport PY_NEW
 from sage.cpython.python_debug cimport if_Py_TRACE_REFS_then_PyObject_INIT
 
@@ -2157,7 +2160,7 @@ cdef PyObject* fast_tp_new(type t, args, kwds) noexcept:
     # Objects from the pool have reference count zero, so this
     # needs to be set in this case.
 
-    new.ob_refcnt = 1
+    Py_SET_REFCNT(<PyObject*>new, 1)
 
     return new
 

src/sage/symbolic/ginac/numeric.cpp

@@ -81,14 +81,14 @@
 
 #define Py_INCREF(op) (                         \
     _Py_INC_REFTOTAL  _Py_REF_DEBUG_COMMA       \
-    ((PyObject*)(op))->ob_refcnt++) ; \
+    Py_SET_REFCNT((PyObject*)(op), Py_REFCNT(op) + 1)) ; \
 std::cerr << "+ " << long(op) << ", " << Py_REFCNT(op) << ", " << Py_TYPE(op)->tp_name << std::endl; std::cerr.flush();
 
 #define Py_DECREF(op)                                   \
     do {                                                \
 std::cerr << "- " << long(op) << ", " << Py_REFCNT(op) << ", " << Py_TYPE(op)->tp_name << std::endl; std::cerr.flush(); \
         if (_Py_DEC_REFTOTAL  _Py_REF_DEBUG_COMMA       \
-        --((PyObject*)(op))->ob_refcnt != 0)            \
+        (Py_SET_REFCNT((PyObject*)(op), Py_REFCNT(op) - 1), Py_REFCNT(op) != 0))            \
             _Py_CHECK_REFCNT(op)                        \
         else                                            \
         _Py_Dealloc((PyObject *)(op));                  \