The previous logic was very wrong, as the check would only occur on each
beat. But that's not how kiai sections work – they can be placed at any
timestamp, even if that doesn't align with a beat.
In addition, the rate limiting has been removed because it didn't exist
on stable and causes some fountains to be missed. Overlap scenarios are
already handled internally by the `StarFountain` class.
Closes https://github.com/ppy/osu/issues/31855.
Rather than control the propagation of the value between the slider and
the textbox, add a property that controls the propagation of the value
between the bindables inside the form control to external bindables.
This will help alleviate issues where the external bindable update
incurs overheads due to having heavy change callbacks attached.