Implement ResetStaticFields for Unity play mode

Added ResetStaticFields method to prevent data persistence in Unity.

Signed-off-by: Vanessa Vinther <7903603+ImDreamerDev@users.noreply.github.com>

Author: ImDreamerDev

sdks/csharp/src/SpacetimeDBClient.cs

@@ -6,6 +6,7 @@
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using UnityEngine;
 using SpacetimeDB.BSATN;
 using SpacetimeDB.ClientApi;
 using Thread = System.Threading.Thread;
@@ -289,6 +290,21 @@ internal struct ParsedMessage
 
         private static readonly Status Committed = new Status.Committed(default);
 
+        /// <summary>
+        /// Resets the static instance to prevent data persistence when Enter Play Mode Options (Disable Domain Reloading) is active.
+        /// RuntimeInitializeOnLoadMethod is used since it is supported in older versions of Unity.
+        /// AutoStaticsCleanup and NoAutoStaticsCleanup is only supported in Unity 6+
+        /// </summary>
+        /// <remarks>
+        /// See the <see href="https://docs.unity3d.com/6000.5/Documentation/Manual/domain-reloading.html">Unity Domain Reloading Manual</see> 
+        /// and the <see href="https://docs.unity3d.com/6000.5/Documentation/ScriptReference/RuntimeInitializeOnLoadMethodAttribute.html">RuntimeInitializeOnLoadMethodAttribute API Docs</see> for details.
+        /// </remarks>
+        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.SubsystemRegistration)]
+        private static void ResetStaticFields()
+        {
+            IsTesting = false;
+        }
+
         /// <summary>
         /// Get a description of a message suitable for storing in the tracker metadata.
         /// </summary>