fix(ab-transport): final review I2 — wire DeviceSessionPool.Shared to the host logger

ConfigureSharedLogger had no production caller, so the pool's only
diagnostics (first-wins options conflicts, scheduler/close failures)
went to NullLogger. DriverFactoryBootstrap now configures it from the
driver registry factory and from the AbCip/AbLegacy probe factories
(admin-only nodes reach the pool only through Test Connect). Wiring tests
reset the pool to a null logger first, so removing the call goes red
(verified).

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

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

@@ -49,6 +49,9 @@ public sealed class DeviceSessionPool
         Shared._logger = loggerFactory.CreateLogger<DeviceSessionPool>();
     }
 
+    /// <summary>Wiring-test hook: the logger this pool currently writes to (final review I2).</summary>
+    internal ILogger Logger => _logger;
+
     /// <summary>Test hook: keys with a live entry.</summary>
     internal int EntryCount { get { lock (_lock) return _entries.Count; } }