fix(ab-transport): RegisterSession carries a zero sender context (found by Task 17 controllogix)

ab_server's RegisterSession sanity check rejects any non-zero sender context
with encapsulation status 1 and a header-only reply, so every native session
against the simulator failed with BadCommunicationError. libplctag sends zero
(logix-register-session.hex); the codec test now matches that capture byte for
byte instead of excluding the context, and a client test pins the zero on the wire.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport/Eip/EncapsulationClient.cs

@@ -82,7 +82,7 @@ public sealed class EncapsulationClient : IAsyncDisposable
         try
         {
             var (header, _) = await client.ExchangeAsync(connected: false,
-                (ctx, _) => EncapsulationCodec.RegisterSession(ctx), timeout, ct).ConfigureAwait(false);
+                (_, _) => EncapsulationCodec.RegisterSession(), timeout, ct).ConfigureAwait(false);
             client.SessionHandle = header.SessionHandle;
             return client;
         }