fix(galaxy): invalidate writer handle caches on session reconnect

Add IGalaxyDataWriter.InvalidateHandleCaches() and call it in
GalaxyDriver.ReopenAsync after RecreateAsync succeeds. Prior to this
fix, GatewayGalaxyDataWriter's _itemHandles and _supervisedHandles
dictionaries survived across reconnects, causing the next write to
skip AddItem and AdviseSupervisory against already-dead handles.

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/Runtime/GalaxyDriverWriteTests.cs

@@ -94,6 +94,9 @@ public sealed class GalaxyDriverWriteTests
             }
             return Task.FromResult<IReadOnlyList<WriteResult>>(results);
         }
+
+        /// <inheritdoc />
+        public void InvalidateHandleCaches() { /* no-op — this fake has no handle caches */ }
     }
 
     private static GalaxyAttribute Attr(string name, int sec)