Closes https://github.com/ppy/osu/issues/26213.
Reproduction scenario: switch audio track in editor after timeline
loads.
Happens because `beatmap.Value.Track.Length` is 0 immediately after a
track switch, until BASS computes the actual track length on the audio
thread.
Yes this is a hack. No I have no better immediate ideas how to address
this otherwise.
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.