feat: Migrate to Python 3.14 (closes #135)

Replace deprecated Python C API calls with modern PyConfig-based initialization:
- PySys_SetArgvEx() -> PyConfig.argv (deprecated since 3.11)
- Py_InspectFlag -> PyConfig.inspect (deprecated since 3.12)

Fix critical memory safety bugs discovered during migration:
- PyColor::from_arg() and PyVector::from_arg() now return new references
  instead of borrowed references, preventing use-after-free when callers
  call Py_DECREF on the result
- GameEngine::testTimers() now holds a local shared_ptr copy during
  callback execution, preventing use-after-free when timer callbacks
  call delTimer() on themselves

Fix double script execution bug with --exec flag:
- Scripts were running twice because GameEngine constructor executed them,
  then main.cpp deleted and recreated the engine
- Now reuses existing engine and just sets auto_exit_after_exec flag

Update test syntax to use keyword arguments for Frame/Caption constructors.

Test results: 127/130 passing (97.7%)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

CMakeLists.txt

@@ -31,7 +31,7 @@ set(LINK_LIBS
 # On Windows, add any additional libs and include directories
 if(WIN32)
     # Windows-specific Python library name (no dots)
-    list(APPEND LINK_LIBS python312)
+    list(APPEND LINK_LIBS python314)
     # Add the necessary Windows-specific libraries and include directories
     # include_directories(path_to_additional_includes)
     # link_directories(path_to_additional_libs)
@@ -39,7 +39,7 @@ if(WIN32)
     include_directories(${CMAKE_SOURCE_DIR}/deps/platform/windows)
 else()
     # Unix/Linux specific libraries
-    list(APPEND LINK_LIBS python3.12 m dl util pthread)
+    list(APPEND LINK_LIBS python3.14 m dl util pthread)
     include_directories(${CMAKE_SOURCE_DIR}/deps/platform/linux)
 endif()