review(Driver.S7.Contracts): first review; gate stringLength check to String type

First review at 7286d320. -002 (Low): stringLength range check now only fires for
S7DataType.String (was rejecting valid non-String equipment-tag blobs). -001 ArrayCount=1
doc fix. -003 (driver-specs.md CpuType omissions) deferred. Consuming Driver.S7.Tests green.

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

@@ -105,7 +105,8 @@ public sealed class S7ProbeOptions
 ///     coils that drive edge-triggered routines in the PLC program.
 /// </param>
 /// <param name="ArrayCount">
-///     Element count when the tag is a 1-D array; <c>null</c> (or <c>&lt;= 1</c>) for a scalar.
+///     Element count when the tag is a 1-D array; <c>null</c> for a scalar. Any value <c>&gt;= 1</c>
+///     (including 1) surfaces as a 1-D OPC UA array node.
 ///     For an equipment tag this is threaded from the <c>TagConfig</c> JSON's <c>arrayLength</c>
 ///     (honoured only when <c>isArray</c> is true) by <see cref="S7EquipmentTagParser"/>. When
 ///     set, the driver issues a single contiguous block read of