remove unnecessary RateLimiterHelper

src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/ConcurrencyLimiter.cs

@@ -32,7 +32,7 @@ public sealed class ConcurrencyLimiter : RateLimiter
         private object Lock => _queue;
 
         /// <inheritdoc />
-        public override TimeSpan? IdleDuration => RateLimiterHelper.GetElapsedTime(_idleSince);
+        public override TimeSpan? IdleDuration => Stopwatch.GetElapsedTime(_idleSince);
         /// <summary>
         /// Initializes the <see cref="ConcurrencyLimiter"/>.
         /// </summary>

src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/FixedWindowRateLimiter.cs

@@ -24,10 +24,10 @@ public sealed class FixedWindowRateLimiter : ReplenishingRateLimiter
 
         /// <summary>
         /// Function to calculate elapsed time from a given tick value.
-        /// Defaults to <see cref="RateLimiterHelper.GetElapsedTime(long?)"/>.
+        /// Defaults to the <c>Stopwatch.GetElapsedTime(long?)</c> extension which returns <see langword="null"/> when the timestamp is <see langword="null"/>.
         /// In tests, this field can be reassigned via reflection to inject custom time behavior without modifying the public API.
         /// </summary>
-        private readonly Func<long?, TimeSpan?> _getElapsedTime = RateLimiterHelper.GetElapsedTime;
+        private readonly Func<long?, TimeSpan?> _getElapsedTime = Stopwatch.GetElapsedTime;
 
         private readonly Timer? _renewTimer;
         private readonly FixedWindowRateLimiterOptions _options;
@@ -39,7 +39,7 @@ public sealed class FixedWindowRateLimiter : ReplenishingRateLimiter
         private static readonly RateLimitLease FailedLease = new FixedWindowLease(false, null);
 
         /// <inheritdoc />
-        public override TimeSpan? IdleDuration => RateLimiterHelper.GetElapsedTime(_idleSince);
+        public override TimeSpan? IdleDuration => Stopwatch.GetElapsedTime(_idleSince);
 
         /// <inheritdoc />
         public override bool IsAutoReplenishing => _options.AutoReplenishment;
@@ -301,7 +301,7 @@ private void ReplenishInternal(long nowTicks)
                     return;
                 }
 
-                if (RateLimiterHelper.GetElapsedTime(_lastReplenishmentTick, nowTicks) < _options.Window && !_options.AutoReplenishment)
+                if (Stopwatch.GetElapsedTime(_lastReplenishmentTick, nowTicks) < _options.Window && !_options.AutoReplenishment)
                 {
                     return;
                 }

src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/RateLimiterHelper.cs

@@ -7,19 +7,17 @@ namespace System.Threading.RateLimiting
 {
     internal static class RateLimiterHelper
     {
-        public static TimeSpan? GetElapsedTime(long? startTimestamp)
+        extension(Stopwatch)
         {
-            if (startTimestamp is null)
+            public static TimeSpan? GetElapsedTime(long? startTimestamp)
             {
-                return null;
-            }
-
-            return Stopwatch.GetElapsedTime(startTimestamp.Value);
-        }
+                if (startTimestamp is null)
+                {
+                    return null;
+                }
 
-        public static TimeSpan GetElapsedTime(long startTimestamp, long endTimestamp)
-        {
-            return Stopwatch.GetElapsedTime(startTimestamp, endTimestamp);
+                return Stopwatch.GetElapsedTime(startTimestamp.Value);
+            }
         }
     }
 }

src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/SlidingWindowRateLimiter.cs

@@ -36,7 +36,7 @@ public sealed class SlidingWindowRateLimiter : ReplenishingRateLimiter
         private static readonly RateLimitLease FailedLease = new SlidingWindowLease(false, null);
 
         /// <inheritdoc />
-        public override TimeSpan? IdleDuration => RateLimiterHelper.GetElapsedTime(_idleSince);
+        public override TimeSpan? IdleDuration => Stopwatch.GetElapsedTime(_idleSince);
 
         /// <inheritdoc />
         public override bool IsAutoReplenishing => _options.AutoReplenishment;
@@ -293,7 +293,7 @@ private void ReplenishInternal(long nowTicks)
                     return;
                 }
 
-                if (RateLimiterHelper.GetElapsedTime(_lastReplenishmentTick, nowTicks) < ReplenishmentPeriod && !_options.AutoReplenishment)
+                if (Stopwatch.GetElapsedTime(_lastReplenishmentTick, nowTicks) < ReplenishmentPeriod && !_options.AutoReplenishment)
                 {
                     return;
                 }

src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/TokenBucketRateLimiter.cs

@@ -34,7 +34,7 @@ public sealed class TokenBucketRateLimiter : ReplenishingRateLimiter
         private static readonly RateLimitLease FailedLease = new TokenBucketLease(false, null);
 
         /// <inheritdoc />
-        public override TimeSpan? IdleDuration => RateLimiterHelper.GetElapsedTime(_idleSince);
+        public override TimeSpan? IdleDuration => Stopwatch.GetElapsedTime(_idleSince);
 
         /// <inheritdoc />
         public override bool IsAutoReplenishing => _options.AutoReplenishment;
@@ -308,7 +308,7 @@ private void ReplenishInternal(long nowTicks)
                 }
                 else
                 {
-                    add = _fillRate * RateLimiterHelper.GetElapsedTime(_lastReplenishmentTick, nowTicks).Ticks;
+                    add = _fillRate * Stopwatch.GetElapsedTime(_lastReplenishmentTick, nowTicks).Ticks;
                 }
 
                 _tokenCount = Math.Min(_options.TokenLimit, _tokenCount + add);