Auto: twincat-2.2 — handle-based access with caching

Closes #311

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/ITwinCATClient.cs

@@ -114,6 +114,16 @@ public interface ITwinCATClient : IDisposable
     ///     decide whether to drill in via their own walker.
     /// </summary>
     IAsyncEnumerable<TwinCATDiscoveredSymbol> BrowseSymbolsAsync(CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     PR 2.2 — wipe process-scoped optional caches (today: the ADS variable-handle
+    ///     cache backing per-tag reads / writes). Surfaces so operators + the future PR
+    ///     2.3 Symbol-Version invalidation listener can flush stale handles after a known
+    ///     online change without forcing a full reconnect. Safe to call mid-traffic — in-flight
+    ///     reads continue to use the handles they already hold; the next read for a symbol
+    ///     will re-resolve. Best-effort wire-side delete; failures are swallowed.
+    /// </summary>
+    Task FlushOptionalCachesAsync();
 }
 
 /// <summary>Opaque handle for a registered ADS notification. <see cref="IDisposable.Dispose"/> tears it down.</summary>