Replace deprecated PyWeakref_GetObject with PyWeakref_GetRef (closes #191)

PyWeakref_GetObject was deprecated in Python 3.13 and will be removed
in 3.15. The new PyWeakref_GetRef API returns a strong reference directly
and uses integer return codes for error handling.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CMakeLists.txt

@@ -16,7 +16,7 @@ endif()
 
 # Add include directories
 include_directories(${CMAKE_SOURCE_DIR}/deps)
-include_directories(${CMAKE_SOURCE_DIR}/deps/libtcod)
+include_directories(SYSTEM ${CMAKE_SOURCE_DIR}/deps/libtcod)
 
 # Python includes: use different paths for Windows vs Linux
 if(MCRF_CROSS_WINDOWS)
@@ -29,7 +29,7 @@ if(MCRF_CROSS_WINDOWS)
     include_directories(${CMAKE_SOURCE_DIR}/deps/cpython/PC)  # For other Windows-specific headers
     # Also include SFML and libtcod Windows headers
     include_directories(${CMAKE_SOURCE_DIR}/__lib_windows/sfml/include)
-    include_directories(${CMAKE_SOURCE_DIR}/__lib_windows/libtcod/include)
+    include_directories(SYSTEM ${CMAKE_SOURCE_DIR}/__lib_windows/libtcod/include)
 else()
     # Native builds (Linux/Windows): use existing Python setup
     include_directories(${CMAKE_SOURCE_DIR}/deps/cpython)

src/PythonObjectCache.cpp

@@ -37,14 +37,16 @@ void PythonObjectCache::registerObject(uint64_t serial, PyObject* weakref) {
 PyObject* PythonObjectCache::lookup(uint64_t serial) {
     if (serial == 0) return nullptr;
 
-    // No mutex needed for read - GIL protects PyWeakref_GetObject
+    // No mutex needed for read - GIL protects PyWeakref_GetRef
     auto it = cache.find(serial);
     if (it != cache.end()) {
-        PyObject* obj = PyWeakref_GetObject(it->second);
+        PyObject* obj = nullptr;
-        if (obj && obj != Py_None) {
+        int result = PyWeakref_GetRef(it->second, &obj);
-            Py_INCREF(obj);
+        if (result == 1 && obj) {
+            // obj is already a strong reference from PyWeakref_GetRef
             return obj;
         }
+        // result == 0: dead reference, result == -1: error
     }
     return nullptr;
 }
@@ -65,11 +67,15 @@ void PythonObjectCache::cleanup() {
 
     auto it = cache.begin();
     while (it != cache.end()) {
-        PyObject* obj = PyWeakref_GetObject(it->second);
+        PyObject* obj = nullptr;
-        if (!obj || obj == Py_None) {
+        int result = PyWeakref_GetRef(it->second, &obj);
+        if (result <= 0) {
+            // Dead reference or error - remove from cache
             Py_DECREF(it->second);
             it = cache.erase(it);
         } else {
+            // Still alive - release the strong reference we obtained
+            Py_DECREF(obj);
             ++it;
         }
     }