Fix interpolating clocks' drift recovery being frame rate dependent

This should largely alleviate any remaining concerns of stutters due to
ppy/osu#22488.

In testing, on both windows and macOS the delay for bass to start
playback is around 10 ms. If there is no interpolation, this would cause
a 10 ms stutter.

I've confirmed that interpolation *does* alleviate this already. The
problem is that depending on the update frame rate, it doesn't do a
great job.

With this change, the drift is spread out over multiple frames, which
should make the issue much less visible to an end user (gameplay will
run slightly slower for a brief period rather than outright stopping).

Author: peppy

osu.Framework/Timing/InterpolatingFramedClock.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Diagnostics;
+using osu.Framework.Utils;
 
 namespace osu.Framework.Timing
 {
@@ -100,11 +101,15 @@ public void ProcessFrame()
 
                 if (IsInterpolating)
                 {
-                    // apply time increase from interpolation.
+                    // Apply time increase from interpolation.
                     currentTime += realtimeClock.ElapsedFrameTime * Rate;
-                    // if we differ from the elapsed time of the source, let's adjust for the difference.
-                    // TODO: this is frame rate depending, and can result in unexpected results.
-                    currentTime += (framedSourceClock.CurrentTime - currentTime) / 8;
+
+                    // Then check the post-interpolated time.
+                    // If we differ from the current time of the source, gradually approach the ground truth.
+                    //
+                    // The remaining error halves every halfTime ms.
+                    // This may need further tweaking to be less discernible by users (upwards, likely?).
+                    currentTime = Interpolation.DampContinuously(currentTime, framedSourceClock.CurrentTime, 50, realtimeClock.ElapsedFrameTime);
 
                     bool withinAllowableError = Math.Abs(framedSourceClock.CurrentTime - currentTime) <= AllowableErrorMilliseconds * Rate;