Make reverse arrow animate faster via divisor specification

Adds MinimumBeatLength to BeatSyncedContainer to make sure things don't get out of hand.

osu.Game/Graphics/Containers/BeatSyncedContainer.cs

@@ -38,6 +38,11 @@ namespace osu.Game.Graphics.Containers
         /// </summary>
         public int Divisor { get; set; } = 1;
 
+        /// <summary>
+        /// An optional minimum beat length. Any beat length below this will be multiplied by two until valid.
+        /// </summary>
+        public double MinimumBeatLength { get; set; }
+
         /// <summary>
         /// Default length of a beat in milliseconds. Used whenever there is no beatmap or track playing.
         /// </summary>
@@ -89,6 +94,9 @@ namespace osu.Game.Graphics.Containers
 
             double beatLength = timingPoint.BeatLength / Divisor;
 
+            while (beatLength < MinimumBeatLength)
+                beatLength *= 2;
+
             int beatIndex = (int)((currentTrackTime - timingPoint.Time) / beatLength) - (effectPoint.OmitFirstBarLine ? 1 : 0);
 
             // The beats before the start of the first control point are off by 1, this should do the trick