This commit changes the semantics of `CurrentFrame` and `NextFrame` of the class.
The ordering of `NextFrame.Time` and `CurrentFrame.Time` was dependent on the current direction.
Now, it should always satisfy `CurrentFrame.Time <= CurrentTime <= NextFrame.Time` except at the start/end.
This change, however, doesn't break existing deriving classes if the template code pattern usage of interpolation is used.
The deriving class code can be simplified due to the elimination of nullable types. I didn't include those changes in this commit.
I removed `StreamingFramedReplayInputHandlerTest` for now, as it is almost-duplicate of `FramedReplayInputHandlerTest`. I'll include more tests in later commits.
This commit fixes#6150.
We're probably not going to need GeneralChecks or BeatmapsetChecks.
The verify tab is only available to a single difficulty at a time, and we already have access to the rest of the set through `IBeatmap`.