Auto: focas-f4a — write infrastructure + per-tag opt-in

Closes #268

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasPmcBitRmwTests.cs

@@ -53,11 +53,18 @@ public sealed class FocasPmcBitRmwTests
     {
         var fake = new PmcRmwFake();
         var factory = new FakeFocasClientFactory { Customise = () => fake };
+        // PMC bit RMW exercises the write path; opt every supplied tag into Writable + flip the
+        // driver-level Writes.Enabled gate so the tests still drive the wire path after F4-a's
+        // safer-by-default flip (issue #268).
+        var writableTags = tags
+            .Select(t => t with { Writable = true })
+            .ToArray();
         var drv = new FocasDriver(new FocasDriverOptions
         {
             Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193")],
-            Tags = tags,
+            Tags = writableTags,
             Probe = new FocasProbeOptions { Enabled = false },
+            Writes = new FocasWritesOptions { Enabled = true },
         }, "drv-1", factory);
         return (drv, fake);
     }