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/AbCipArrayTests.cs

@@ -156,6 +156,37 @@ public sealed class AbCipArrayTests
         snapshots.Single().Value.ShouldNotBeOfType<int[]>();
     }
 
+    /// <summary>
+    ///     Driver.AbCip-016 — a DECLARED UDT member that is a 1-D array (<c>Setpoints : REAL[4]</c>)
+    ///     must READ as a typed CLR array, matching the array node it discovers as. Before the fix
+    ///     the member fan-out in <c>InitializeAsync</c> dropped the member's <c>ElementCount</c> /
+    ///     <c>IsArray</c>, so the fanned-out runtime definition defaulted to scalar and the read
+    ///     returned a single element (or null) instead of the array — a declared-type-vs-runtime-value
+    ///     mismatch.
+    /// </summary>
+    [Fact]
+    public async Task Declared_udt_array_member_reads_as_typed_array()
+    {
+        var (drv, factory) = NewDriver(
+            new AbCipTagDefinition("Motor", "ab://10.0.0.5/1,0", "Motor", AbCipDataType.Structure,
+                Members:
+                [
+                    new AbCipStructureMember("Setpoints", AbCipDataType.Real, ElementCount: 4),
+                    new AbCipStructureMember("Speed", AbCipDataType.DInt),
+                ]));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new ArrayFakeAbCipTag(p, new float[] { 1.5f, 2.5f, 3.5f, 4.5f });
+
+        var snapshots = await drv.ReadAsync(["Motor.Setpoints"], CancellationToken.None);
+
+        snapshots.Single().StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        var value = snapshots.Single().Value.ShouldBeOfType<float[]>();
+        value.ShouldBe([1.5f, 2.5f, 3.5f, 4.5f]);
+        // The fanned-out member runtime must thread the member's element count to libplctag.
+        factory.Tags["Motor.Setpoints"].CreationParams.ElementCount.ShouldBe(4);
+        factory.Tags["Motor.Setpoints"].CreationParams.IsArray.ShouldBeTrue();
+    }
+
     // ---- Resolver: arrayLength threading ----
 
     /// <summary>The equipment-tag resolver threads arrayLength into the def's ElementCount.</summary>