Fix second-pass review findings: subscription leak on rebuild, metrics accuracy, and MxAccess startup recovery

- Preserve and replay subscription ref counts across address space rebuilds to prevent MXAccess subscription leaks
- Mark read timeouts and write failures as unsuccessful in PerformanceMetrics for accurate health reporting
- Add deferred MxAccess reconnect path when initial connection fails at startup
- Update code review document with verified completions and new findings
- Add covering tests for all fixes

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

tests/ZB.MOM.WW.LmxOpcUa.Tests/Helpers/FakeMxProxy.cs

@@ -29,6 +29,7 @@ namespace ZB.MOM.WW.LmxOpcUa.Tests.Helpers
         public int UnregisterCallCount { get; private set; }
         public bool ShouldFailRegister { get; set; }
         public bool ShouldFailWrite { get; set; }
+        public bool SkipWriteCompleteCallback { get; set; }
         public int WriteCompleteStatus { get; set; } = 0; // 0 = success
 
         public int Register(string clientName)
@@ -87,7 +88,8 @@ namespace ZB.MOM.WW.LmxOpcUa.Tests.Helpers
                 status[0].success = 0;
                 status[0].detail = (short)WriteCompleteStatus;
             }
-            OnWriteComplete?.Invoke(_connectionHandle, itemHandle, ref status);
+            if (!SkipWriteCompleteCallback)
+                OnWriteComplete?.Invoke(_connectionHandle, itemHandle, ref status);
         }
 
         /// <summary>