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`.
While it is the case for the existing official Skills, Skill implementations shouldn't be required to conform to a strain based approach.
There are other valid approaches to calculating skill difficulty that can be supported by abstracting the strain logic into its own StrainSkill class.
As strains are an implementation detail of the current Skill calculations, it makes sense that strain related logic should be encapsulated within the Skill class.
There is no reason we should be limiting skills to knowing only the previous 2 objects. This originally existed as an angle implementation detail of the original pp+ codebase which made its way here, but didn't get used in the same way.
