feat(lmxproxy): phase 5 — client core (ILmxProxyClient, connection, read/write/subscribe)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lmxproxy/src/ZB.MOM.WW.LmxProxy.Client/LmxProxyClient.ISubscription.cs

@@ -0,0 +1,13 @@
+namespace ZB.MOM.WW.LmxProxy.Client;
+
+public partial class LmxProxyClient
+{
+    /// <summary>
+    /// Represents an active tag subscription. Dispose to unsubscribe.
+    /// </summary>
+    public interface ISubscription : IDisposable
+    {
+        /// <summary>Asynchronous disposal with cancellation support.</summary>
+        Task DisposeAsync();
+    }
+}