Previously the slider path length would be snapped using the current
beat snap setting on *every* change of the slider path. As it turns out
this is unexpected behaviour in some situations (e.g. when reversing a
path, which is expected to preserve the previous duration, even though
the slider may be technically "unsnapped" at that point in time due to a
different beat snap setting being selected afterwards).
This is quite a breaking change, but I think it is beneficial due to the large amount of usage of this class.
I originally intended just to remove the allocations of the two delegates handling the `Changed` flow internally, but as nothing was really using the bindables for anything more than a general "point has changed" case, this felt like a better direction.
