Auto: s7-a4 — array tags (ValueRank=1)

- S7TagDefinition gets optional ElementCount; >1 marks the tag as a 1-D array.
- ReadOneAsync / WriteOneAsync: one byte-range Read/WriteBytesAsync covering
  N × elementBytes, sliced/packed client-side via the existing big-endian scalar
  codecs and S7DateTimeCodec.
- DiscoverAsync surfaces IsArray=true and ArrayDim=ElementCount → ValueRank=1.
- Init-time validation (now ahead of TCP open) caps ElementCount at 8000 and
  rejects unsupported element types: STRING/WSTRING/CHAR/WCHAR (variable-width)
  and BOOL (packed-bit layout) — both follow-ups.
- Supported element types: Byte, Int16/UInt16, Int32/UInt32, Int64/UInt64,
  Float32, Float64, Date, Time, TimeOfDay.

Closes #290

src/ZB.MOM.WW.OtOpcUa.Driver.S7/S7DriverOptions.cs

@@ -95,13 +95,23 @@ public sealed class S7ProbeOptions
 ///     value can be written again without side-effects. Unsafe: M (merker) bits or Q (output)
 ///     coils that drive edge-triggered routines in the PLC program.
 /// </param>
+/// <param name="ElementCount">
+///     Optional 1-D array length. <c>null</c> (or <c>1</c>) = scalar tag; <c>&gt; 1</c> = array.
+///     The driver issues one byte-range read covering <c>ElementCount × bytes-per-element</c>
+///     and slices client-side via the existing scalar codec. Multi-dim arrays are deferred;
+///     array-of-UDT lands with PR-S7-D2. Variable-width element types
+///     (STRING/WSTRING/CHAR/WCHAR) and BOOL (packed bits) are rejected at init time —
+///     they need bespoke layout handling and are tracked as a follow-up. Capped at 8000 to
+///     keep the byte-range request inside a single S7 PDU envelope.
+/// </param>
 public sealed record S7TagDefinition(
     string Name,
     string Address,
     S7DataType DataType,
     bool Writable = true,
     int StringLength = 254,
-    bool WriteIdempotent = false);
+    bool WriteIdempotent = false,
+    int? ElementCount = null);
 
 public enum S7DataType
 {