- Add native CGL backend using macOS OpenGL framework via ctypes
- Skip EGL on macOS (DarwinPlatform lacks EGL, and importing it
poisons PyOpenGL platform selection for OSMesa)
- Move _vao init before backend init to prevent AttributeError on retry
- Move _initialized flag to end of __init__ so failed inits can retry
Amp-Thread-ID: https://ampcode.com/threads/T-019c6eaf-742b-7009-b4f1-d59b28a4da20