review(Driver.TwinCAT): thread ArrayLength through factory DTO (Medium)

Re-review at 7286d320. -017 (Medium): TwinCATTagDto lacked ArrayLength, so JSON-authored
pre-declared array tags were silently scalar (Phase-4c array path dead for them). Fix:
add ArrayLength to the DTO + thread through BuildTag with positive-value guard + TDD.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/TwinCATDriverFactoryExtensions.cs

@@ -109,7 +109,11 @@ public static class TwinCATDriverFactoryExtensions
                 $"TwinCAT tag '{t.Name}' in '{driverInstanceId}' missing SymbolPath"),
             DataType: dataType,
             Writable: t.Writable ?? true,
-            WriteIdempotent: t.WriteIdempotent ?? false);
+            WriteIdempotent: t.WriteIdempotent ?? false,
+            // Driver.TwinCAT-017: thread arrayLength through so JSON-authored pre-declared tags can
+            // declare 1-D arrays (Phase 4c). Only positive values are honoured; null / non-positive
+            // keeps the scalar default (ArrayLength: null on TwinCATTagDefinition).
+            ArrayLength: t.ArrayLength is > 0 ? t.ArrayLength : null);
     }
 
     private static T ParseEnum<T>(string? raw, string? tagName, string driverInstanceId, string field)
@@ -184,6 +188,14 @@ public static class TwinCATDriverFactoryExtensions
 
         /// <summary>Gets or sets a value indicating whether writes are idempotent.</summary>
         public bool? WriteIdempotent { get; init; }
+
+        /// <summary>
+        ///     Optional 1-D array element count. When positive, the tag is a 1-D array of this
+        ///     many <see cref="DataType"/> elements — drives <c>IsArray</c>/<c>ArrayDim</c> at
+        ///     discovery and a native ADS array read at runtime (Phase 4c, Driver.TwinCAT-017).
+        ///     <c>null</c> or non-positive = scalar (the default).
+        /// </summary>
+        public int? ArrayLength { get; init; }
     }
 
     internal sealed class TwinCATProbeDto