Implement lazy timed difficulty calculation

Author: minisbett

osu.Game/Rulesets/Difficulty/DifficultyCalculator.cs

@@ -94,6 +94,9 @@ public DifficultyAttributes Calculate([NotNull] IEnumerable<Mod> mods, Cancellat
         /// <summary>
         /// Calculates the difficulty of the beatmap with no mods applied and returns a set of <see cref="TimedDifficultyAttributes"/> representing the difficulty at every relevant time value in the beatmap.
         /// </summary>
+        /// <remarks>
+        /// Unless a <paramref name="cancellationToken"/> is specified, calculation times out after 10 seconds.
+        /// </remarks>
         /// <param name="cancellationToken">The cancellation token.</param>
         /// <returns>The set of <see cref="TimedDifficultyAttributes"/>.</returns>
         public List<TimedDifficultyAttributes> CalculateTimed(CancellationToken cancellationToken = default)
@@ -102,12 +105,15 @@ public List<TimedDifficultyAttributes> CalculateTimed(CancellationToken cancella
         /// <summary>
         /// Calculates the difficulty of the beatmap using a specific mod combination and returns a set of <see cref="TimedDifficultyAttributes"/> representing the difficulty at every relevant time value in the beatmap.
         /// </summary>
+        /// <remarks>
+        /// Unless a <paramref name="cancellationToken"/> is specified, calculation times out after 10 seconds.
+        /// </remarks>
         /// <param name="mods">The mods that should be applied to the beatmap.</param>
         /// <param name="cancellationToken">The cancellation token.</param>
         /// <returns>The set of <see cref="TimedDifficultyAttributes"/>.</returns>
         public List<TimedDifficultyAttributes> CalculateTimed([NotNull] IEnumerable<Mod> mods, CancellationToken cancellationToken = default)
         {
-            List<TimedDifficultyAttributes> list = [];
+            List<TimedDifficultyAttributes> attribs = [];
             using var timedCancellationSource = new CancellationTokenSource(TimeSpan.FromSeconds(10));
 
             if (!cancellationToken.CanBeCanceled)
@@ -116,17 +122,18 @@ public List<TimedDifficultyAttributes> CalculateTimed([NotNull] IEnumerable<Mod>
             foreach (var timedAttr in CalculateTimedLazy(mods, cancellationToken))
             {
                 cancellationToken.ThrowIfCancellationRequested();
-                list.Add(timedAttr);
+                attribs.Add(timedAttr);
             }
 
-            return list;
+            return attribs;
         }
 
         /// <summary>
         /// Lazily calculates the difficulty of the beatmap on-demand using a specific mod combination and yields <see cref="TimedDifficultyAttributes"/> representing the difficulty until every relevant time value in the beatmap.
         /// </summary>
         /// <remarks>
-        /// Preprocessing is done before this method returns.
+        /// 1. Preprocessing is done before this method returns.<br />
+        /// 2. Cancelling the <paramref name="cancellationToken"/> will throw while enumerating.
         /// </remarks>
         /// <param name="mods">The mods that should be applied to the beatmap.</param>
         /// <param name="cancellationToken">The cancellation token.</param>
@@ -157,6 +164,7 @@ IEnumerable<TimedDifficultyAttributes> enumerateTimed()
                     {
                         foreach (var skill in skills)
                         {
+                            cancellationToken.ThrowIfCancellationRequested();
                             skill.Process(difficultyObjects[currentIndex]);
                         }