feat: Non-deterministic debug simulator in UnityTransport [MTT-4592] (#2196)

* feat: Non-deterministic debug simulator in UnityTransport [MTT-4592]

* Add PR number to CHANGELOG entry

Author: simon-lemay-unity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -9,6 +9,10 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ## [Unreleased]
 
+### Changed
+
+- The debug simulator in `UnityTransport` is now non-deterministic. Its random number generator used to be seeded with a constant value, leading to the same pattern of packet drops, delays, and jitter in every run. (#2196)
+
 ### Fixed
 
 - Fixed ILPP `TypeLoadException` on WebGL on MacOS Editor and potentially other platforms. (#2199)

com.unity.netcode.gameobjects/Runtime/Transports/UTP/UnityTransport.cs

@@ -337,7 +337,7 @@ public struct SimulatorParameters
             PacketDropRate = 0
         };
 
-        internal uint DebugSimulatorRandomSeed { get; set; } = 0;
+        internal uint? DebugSimulatorRandomSeed { get; set; } = null;
 
         private struct PacketLossCache
         {
@@ -1325,7 +1325,7 @@ private void ConfigureSimulator()
                 packetDelayMs: DebugSimulator.PacketDelayMS,
                 packetJitterMs: DebugSimulator.PacketJitterMS,
                 packetDropPercentage: DebugSimulator.PacketDropRate,
-                randomSeed: DebugSimulatorRandomSeed
+                randomSeed: DebugSimulatorRandomSeed ?? (uint)System.Diagnostics.Stopwatch.GetTimestamp()
 #if UTP_TRANSPORT_2_0_ABOVE
                 , mode: ApplyMode.AllPackets
 #endif