Add task extensions for timeouts

Marc's working on connection code so we'll plug these in after.

StackExchange.Redis/StackExchange/Redis/TaskExtensions.cs

 using System;
 using System.Runtime.CompilerServices;
+using System.Threading;
 using System.Threading.Tasks;
 
 namespace StackExchange.Redis
@@ -27,5 +28,36 @@ public static Task<T> ObserveErrors<T>(this Task<T> task)
         public static ConfiguredTaskAwaitable ForAwait(this Task task) => task.ConfigureAwait(false);
         public static ConfiguredTaskAwaitable<T> ForAwait<T>(this Task<T> task) => task.ConfigureAwait(false);
         public static ConfiguredValueTaskAwaitable<T> ForAwait<T>(this ValueTask<T> task) => task.ConfigureAwait(false);
+
+        // Inspired from https://github.com/dotnet/corefx/blob/81a246f3adf1eece3d981f1d8bb8ae9de12de9c6/src/Common/tests/System/Threading/Tasks/TaskTimeoutExtensions.cs#L15-L43
+        // Licensed to the .NET Foundation under one or more agreements.
+        // The .NET Foundation licenses this file to you under the MIT license.
+        public static async Task TimeoutAfter(this Task task, int millisecondsTimeout, string message)
+        {
+            var cts = new CancellationTokenSource();
+            if (task == await Task.WhenAny(task, Task.Delay(millisecondsTimeout, cts.Token)).ConfigureAwait(false))
+            {
+                cts.Cancel();
+                await task.ConfigureAwait(false);
+            }
+            else
+            {
+                throw new TimeoutException(message);
+            }
+        }
+
+        public static async Task<TResult> TimeoutAfter<TResult>(this Task<TResult> task, int millisecondsTimeout, string message)
+        {
+            var cts = new CancellationTokenSource();
+            if (task == await Task<TResult>.WhenAny(task, Task<TResult>.Delay(millisecondsTimeout, cts.Token)).ConfigureAwait(false))
+            {
+                cts.Cancel();
+                return await task.ConfigureAwait(false);
+            }
+            else
+            {
+                throw new TimeoutException(message);
+            }
+        }
     }
 }