Optimise bin selection in difficulty calculation

[WilliamQiufeng]

Importing Force! Full Album now takes 10s than 2 minutes.

...
            var valuesInBin = StrainSolverData.Where(s => s.StartTime >= i && s.StartTime < i + binSize).ToList();
...

This line is very inefficient.
My PR optimises it so that CalculateOverallDifficulty() is now $O(n)$ instead of $O(n^2)$, where n is StrainSolverData.Count.

The following patch lets you better check if there's any bug with this change.

Debug_Diffcalc_bin_optimization.patch

I wrote a verification tool:
https://github.com/WilliamQiufeng/Quaver.VerifyOptimizedBinDiffCalc

git clone --recurse-submodules https://github.com/WilliamQiufeng/Quaver.VerifyOptimizedBinDiffCalc
cd Quaver.VerifyOptimizedBinDiffCalc
dotnet run --project RecalcTest <path-to-song-dir>

The optimization will for now only apply to 4K maps due to a bug described in #181