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
