Auto: twincat-1.3 — bit-indexed BOOL writes (RMW)

Replace the NotSupportedException at AdsTwinCATClient.WriteValueAsync
for bit-indexed BOOL writes with a read-modify-write path:

  1. Strip the trailing .N selector from the symbol path.
  2. Read the parent as UDINT.
  3. Set or clear bit N via the standard mask.
  4. Write the parent back.

Concurrent bit writers against the same parent serialise through a
per-parent SemaphoreSlim cached in a ConcurrentDictionary (never
removed — bounded by writable-bit-tag cardinality). Mirrors the AbCip /
Modbus / FOCAS bit-RMW pattern shipped in #181 pass 1.

The path-stripping (TryGetParentSymbolPath) and mask helper (ApplyBit)
are exposed as internal statics so tests can pin the pure logic without
needing a real ADS target. The FakeTwinCATClient mirrors the same RMW
semantics so driver-level round-trip tests assert the parent-word state.

Closes #307

tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/FakeTwinCATClient.cs

@@ -41,7 +41,25 @@ internal class FakeTwinCATClient : ITwinCATClient
     {
         if (ThrowOnWrite) throw Exception ?? new InvalidOperationException();
         WriteLog.Add((symbolPath, type, bitIndex, value));
-        Values[symbolPath] = value;
+
+        // Model the parent-word RMW path the production AdsTwinCATClient performs for
+        // bit-indexed BOOL writes so driver-level tests can assert the resulting parent state.
+        if (bitIndex is int bit && type == TwinCATDataType.Bool)
+        {
+            var parentPath = AdsTwinCATClient.TryGetParentSymbolPath(symbolPath);
+            if (parentPath is not null)
+            {
+                var current = Values.TryGetValue(parentPath, out var p) && p is not null
+                    ? Convert.ToUInt32(p) : 0u;
+                Values[parentPath] = AdsTwinCATClient.ApplyBit(
+                    current, bit, Convert.ToBoolean(value));
+            }
+        }
+        else
+        {
+            Values[symbolPath] = value;
+        }
+
         var status = WriteStatuses.TryGetValue(symbolPath, out var s) ? s : TwinCATStatusMapper.Good;
         return Task.FromResult(status);
     }