Implement deferred core utility parity APIs/tests and refresh tracking artifacts

dotnet/src/ZB.MOM.NatsNet.Server/Internal/AccessTimeService.cs

@@ -25,6 +25,18 @@ public static class AccessTimeService
         // Mirror Go's init(): nothing to pre-allocate in .NET.
     }
 
+    /// <summary>
+    /// Explicit init hook for Go parity.
+    /// Mirrors package <c>init()</c> in server/ats/ats.go.
+    /// This method is intentionally idempotent.
+    /// </summary>
+    public static void Init()
+    {
+        // Ensure a non-zero cached timestamp is present.
+        var now = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() * 1_000_000L;
+        Interlocked.CompareExchange(ref _utime, now, 0);
+    }
+
     /// <summary>
     /// Registers a user. Starts the background timer when the first registrant calls this.
     /// Each call to <see cref="Register"/> must be paired with a call to <see cref="Unregister"/>.