Move OpcUaClientDriverOptions and all companion enums (OpcUaTargetNamespaceKind,
OpcUaSecurityMode, OpcUaSecurityPolicy, OpcUaAuthType) to a new
Driver.OpcUaClient.Contracts sibling project. The options file had no
using directives — all types were defined in the same file — so no
NuGet mirror enum pattern was required.
Convert two doc-comment references:
<see cref="OpcUaClientDriver.InitializeAsync"/> → <c>OpcUaClientDriver.InitializeAsync</c>
<see cref="OpcUaClientDriver.ValidateNamespaceKind"/> → <c>OpcUaClientDriver.ValidateNamespaceKind</c>
per the approved decision — no compilable usings were present.
The runtime Driver.OpcUaClient project gains a ProjectReference to .Contracts;
the .slnx is updated accordingly.
Joseph Doherty