feat(ablegacy): PCCC multi-element file array read + IsArray discovery

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Contracts/AbLegacyDriverOptions.cs

@@ -41,13 +41,31 @@ public sealed record AbLegacyDeviceOptions(
 ///     One PCCC-backed OPC UA variable. <paramref name="Address"/> is the canonical PCCC
 ///     file-address string that parses via <c>AbLegacyAddress.TryParse</c>.
 /// </summary>
+/// <param name="ArrayLength">
+///     Element count when the tag addresses a multi-element span of a PCCC data file (e.g. an
+///     <c>N7</c> integer file is inherently up to 256 words); <see langword="null"/> for a scalar.
+///     A PCCC data file holds at most <see cref="AbLegacyArray.MaxElements"/> (256) elements, so a
+///     value above that is clamped where it is materialised/read. <c>1</c> reads as a scalar.
+/// </param>
 public sealed record AbLegacyTagDefinition(
     string Name,
     string DeviceHostAddress,
     string Address,
     AbLegacyDataType DataType,
     bool Writable = true,
-    bool WriteIdempotent = false);
+    bool WriteIdempotent = false,
+    int? ArrayLength = null);
+
+/// <summary>PCCC array-tag constants shared by the parser, discovery, and read paths.</summary>
+public static class AbLegacyArray
+{
+    /// <summary>
+    ///     Maximum element count for a single PCCC data file. The PCCC/DF1 protocol addresses a
+    ///     data file element with a single byte sub-element offset, so a file holds at most 256
+    ///     elements (words for N/B/I/O/S/A, 32-bit elements for L/F). Array tags clamp to this.
+    /// </summary>
+    public const int MaxElements = 256;
+}
 
 public sealed class AbLegacyProbeOptions
 {