handleZoom
Handles a zoom operation by delegating to the registered zoom handler.
Called by zoom button clicks in AndroidAutoNavigationScreen (via AndroidAutoSurfaceManager.zoomIn/zoomOut convenience methods).
The registered handler (in AndroidAutoSurfaceCallback) reads the live camera state from the MapView and applies zoom at the correct position.
This is safe to call even if the handler is not set (no-op).
Parameters
zoomIn
true to zoom in (increase zoom level), false to zoom out (decrease)