chore: initialize standalone UPM package

Runtime/Network/IShrinkModNetworkTransport.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace ShrinkModFramework
+{
+    public interface IShrinkModNetworkTransport
+    {
+        bool IsServer { get; }
+        bool IsClient { get; }
+
+        event Action<ShrinkModNetworkEnvelope> OnEnvelopeReceived;
+
+        void Send(ShrinkModNetworkEnvelope envelope);
+    }
+}