Adds an opt-in pass-3 walk of the upstream TypesFolder (i=86) so the OPC UA
Client driver can mirror upstream type definitions into the local address
space. Honours the curation rules from PR-7 (#359). Structural mirror only —
binary-encoding priming via LoadDataTypeSystem is tracked as a follow-up
because that helper was removed from the public ISession surface in
OPCFoundation.NetStandard 1.5.378+.
- IAddressSpaceBuilder.RegisterTypeNode (default no-op for back-compat)
- MirroredTypeNodeInfo + MirroredTypeKind in Core.Abstractions
- OpcUaClientDriverOptions.MirrorTypeDefinitions (default false)
- DiscoverAsync pass-3: FetchTypeTreeAsync + recursive HasSubtype walk per
branch (ObjectTypes/VariableTypes/DataTypes/ReferenceTypes), best-effort
IsAbstract read, IncludePaths/ExcludePaths still applied
- 6 new unit tests; all 153 OpcUaClient unit tests pass
Closes#280
