feat(network)!: add v2 framing, pooled buffers and bounded dispatch

Runtime/Transport/Abstractions/IShrinkNetworkAsyncTransport.cs

@@ -1,4 +1,6 @@
 using Cysharp.Threading.Tasks;
+using System;
+using System.Threading;
 
 namespace ShrinkNetwork
 {
@@ -6,4 +8,10 @@ namespace ShrinkNetwork
     {
         UniTask SendAsync(long sessionId, byte[] packetData);
     }
+
+    /// <summary>Borrowed memory remains owned by caller until SendAsync completes, faults or cancels.</summary>
+    public interface IShrinkNetworkMemoryTransport : IShrinkNetworkAsyncTransport
+    {
+        UniTask SendAsync(long sessionId, ReadOnlyMemory<byte> packetData, CancellationToken cancellationToken = default);
+    }
 }