This causes the focal point zooming to not work (as the focal point is
lost). There's no need to handle ongoing changes to
`BeatmapInfo.TimelineZoom` because it is not a property which is changed
at runtime.
Alternate method is to expose a `SnapDistancesChanged` event in
`IPositionSnapProvider` instead, but I chose this way as an analogue to
`IBeatSnapProvider.BeatDivisor`, which might even make sense to be
exposed as `BindableBeatDivisor` instead of caching that separately.