review(Driver.AbCip): fix declared UDT array members read as scalar (Medium)

Re-review at 7286d320. AbCip-016 (Medium): two cooperating defects made a declared array
member (e.g. REAL[4]) read one scalar/null — fan-out dropped ElementCount/IsArray, and
UdtMemberLayout.TryBuild ignored array members (mis-placing later members). Fix: thread
array shape through fan-out + opt whole-UDT grouping out when any member is an array + TDD.
AbCip-017 (severity-read StatusCode, Low) deferred.

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipUdtMemberLayoutTests.cs

@@ -74,4 +74,29 @@ public sealed class AbCipUdtMemberLayoutTests
     {
         AbCipUdtMemberLayout.TryBuild(Array.Empty<AbCipStructureMember>()).ShouldBeNull();
     }
+
+    /// <summary>
+    ///     Driver.AbCip-016 — declaration-only layout returns null when any member is a 1-D array.
+    ///     The whole-UDT grouped read path decodes one scalar per member at its offset
+    ///     (<c>DecodeValueAt</c>) and cannot return an array, and the scalar-size cursor advance
+    ///     would mis-place every member after the array. Opting the whole group out sends array
+    ///     members through the per-tag read path, which reads them as typed arrays.
+    /// </summary>
+    [Fact]
+    public void Returns_Null_When_A_Member_Is_An_Array()
+    {
+        // Explicit IsArray flag (even a 1-element array).
+        AbCipUdtMemberLayout.TryBuild(new[]
+        {
+            new AbCipStructureMember("A", AbCipDataType.DInt),
+            new AbCipStructureMember("Buf", AbCipDataType.Real, IsArray: true, ElementCount: 1),
+        }).ShouldBeNull();
+
+        // Legacy ElementCount > 1 with the flag unset.
+        AbCipUdtMemberLayout.TryBuild(new[]
+        {
+            new AbCipStructureMember("A", AbCipDataType.DInt),
+            new AbCipStructureMember("Setpoints", AbCipDataType.Real, ElementCount: 4),
+        }).ShouldBeNull();
+    }
 }