trim (#435)

Author: bitfaster

BitFaster.Caching/Lfu/ConcurrentLfu.cs

@@ -188,9 +188,13 @@ public void Trim(int itemCount)
                 TakeCandidatesInLruOrder(this.probationLru, candidates, itemCount);
                 TakeCandidatesInLruOrder(this.protectedLru, candidates, itemCount);
                 TakeCandidatesInLruOrder(this.windowLru, candidates, itemCount);
-            }
-
+            }
+
+#if NET6_0_OR_GREATER
+            foreach (var candidate in CollectionsMarshal.AsSpan(candidates))
+#else
             foreach (var candidate in candidates)
+#endif
             {
                 this.TryRemove(candidate.Key);
             }