changed magnifier uninitialize (#20069)
fix #20068
Summary of the issue:
Stopping and restarting the fullscreen magnifier fails with OSError: [WinError 0] from MagSetFullscreenTransform.
Description of user facing changes:
The fullscreen magnifier can now be stopped and restarted reliably.
Description of developer facing changes:
_stopMagnifier() no longer calls MagUninitialize(), only resets the transform to neutral
New _finalUninitializeNativeMagnification() called from terminate() on NVDA shutdown
_nativeApiInitialized flag ensures MagInitialize() is only called once per session
Description of development approach:
The MagInitialize → MagUninitialize → MagInitialize cycle within the same process causes MagSetFullscreenTransform to silently return FALSE with no error code. The fix keeps the API initialized for the NVDA session lifetime and defers MagUninitialize() to shutdown.
