Update C# benchmark Program.cs to fix benchmark timing collection. (#4478)

Update benchmark timing collection code in RedisBenchmark to better use Stopwatch.

Changed use of Stopwatch.Start() to Stopwatch.Restart(). The Restart() method zeroes out the timer for each iteration. The prior code would accumulate time across all iterations.

Converted the time collection to use Stopwatch.Elapsed.TotalMilliseconds, as this provides a double value and is the proper value to use in this case.

Signed-off-by: L Joseph McGuinness <ljosephmcguinness@gmail.com>
Co-authored-by: Joseph Brinkman <joe.brinkman@improving.com>

Author: ljmcg

benchmarks/csharp/Program.cs

@@ -123,7 +123,7 @@ private static async Task RedisBenchmark(
             int index = (int)(s_started_tasks_counter % clients.Length);
             ClientWrapper client = clients[index];
             ChosenAction action = ChooseAction();
-            stopwatch.Start();
+            stopwatch.Restart();
             switch (action)
             {
                 case ChosenAction.GET_EXISTING:
@@ -140,7 +140,7 @@ private static async Task RedisBenchmark(
             }
             stopwatch.Stop();
             ConcurrentBag<double> latency_list = action_latencies[action];
-            latency_list.Add(((double)stopwatch.ElapsedMilliseconds) / 1000);
+            latency_list.Add(stopwatch.Elapsed.TotalMilliseconds);
         } while (s_started_tasks_counter < total_commands);
     }