Auto: abcip-2.3 — descriptions to OPC UA Description

Threads tag/UDT-member descriptions captured by the L5K (#346) and L5X
(#347) parsers through AbCipTagDefinition + AbCipStructureMember into
DriverAttributeInfo, so the address-space builder sets the OPC UA
Description attribute on each Variable node. L5kMember and L5xParser
also now capture per-member descriptions (via the (Description := "...")
attribute block on L5K and the <Description> child on L5X), and
L5kIngest forwards them. DriverNodeManager surfaces
DriverAttributeInfo.Description as the Variable's Description property.

Description is added as a trailing optional parameter on
DriverAttributeInfo (default null) so every other driver continues
to construct the record unchanged.

Closes #231

src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/DriverNodeManager.cs

@@ -178,6 +178,13 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
                 NodeId = new NodeId(attributeInfo.FullName, NamespaceIndex),
                 BrowseName = new QualifiedName(browseName, NamespaceIndex),
                 DisplayName = new LocalizedText(displayName),
+                // Per Task #231 — surface the driver-supplied tag description as the OPC UA
+                // Description attribute on the Variable node. Drivers that don't carry
+                // descriptions pass null, leaving Description unset (the stack defaults to
+                // an empty LocalizedText, matching prior behaviour).
+                Description = string.IsNullOrEmpty(attributeInfo.Description)
+                    ? null
+                    : new LocalizedText(attributeInfo.Description),
                 DataType = MapDataType(attributeInfo.DriverDataType),
                 ValueRank = attributeInfo.IsArray ? ValueRanks.OneDimension : ValueRanks.Scalar,
                 // Historized attributes get the HistoryRead access bit so the stack dispatches