zoomTo method
Sets the zoom to an absolute target, clamped to [minZoom, maxZoom] by
the Controller. A no-op when not isAttached.
The Controller only zooms multiplicatively (relative to the zoom captured
by startZoom), so this asks it to scale from the current zoom to target;
the clamp still applies. A current zoom of 0 (only reachable with a
minZoom <= 0) has no defined scale to target, so it is left untouched.
Implementation
void zoomTo(double target) {
final inner = _inner;
if (inner == null) return;
final current = inner.zoom;
if (current <= 0) return;
inner.startZoom();
inner.updateZoom(target / current);
}