fix(client-shared): resolve Low code-review findings (Client.Shared-003,004,009,010,011)

- Client.Shared-003: DefaultSessionAdapter.WriteValueAsync / CallMethodAsync
  guard against null/empty Results and throw ServiceResultException with
  the response's ServiceResult code instead of indexing into a missing
  list.
- Client.Shared-004: DefaultSessionAdapter.CloseAsync / HistoryReadRawAsync
  / HistoryReadAggregateAsync use the Session.*Async overloads and honour
  the caller's CancellationToken.
- Client.Shared-009: AcknowledgeAlarmAsync returns the underlying
  ServiceResultException.StatusCode on failure instead of always Good;
  IOpcUaClientService doc updated to describe the new contract.
- Client.Shared-010: ConnectionSettings.CertificateStorePath defaults to
  empty; DefaultApplicationConfigurationFactory resolves the canonical
  PKI path lazily, so per-failover ConnectionSettings copies don't hit
  the filesystem.
- Client.Shared-011: added the alarm-fallback regression test, extracted
  EndpointSelector as a pure static, and added EndpointSelectorTests
  covering security-mode match, Basic256Sha256 preference, fallback,
  diagnostics, hostname rewrite, and null/empty guards.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Client/ZB.MOM.WW.OtOpcUa.Client.Shared.Tests/Fakes/FakeSessionAdapter.cs

@@ -168,10 +168,25 @@ internal sealed class FakeSessionAdapter : ISessionAdapter
         }
     }
 
+    /// <summary>
+    /// Number of times <see cref="CallMethodAsync"/> was invoked so tests can assert
+    /// acknowledgment workflows reached the session adapter.
+    /// </summary>
+    public int CallMethodCount { get; private set; }
+
+    /// <summary>
+    /// When set, <see cref="CallMethodAsync"/> throws this exception — used to simulate
+    /// a bad method call status surfacing as a <see cref="ServiceResultException"/>.
+    /// </summary>
+    public Exception? CallMethodException { get; set; }
+
     /// <inheritdoc />
     public Task<IList<object>?> CallMethodAsync(NodeId objectId, NodeId methodId, object[] inputArguments,
         CancellationToken ct = default)
     {
+        CallMethodCount++;
+        if (CallMethodException != null)
+            throw CallMethodException;
         return Task.FromResult<IList<object>?>(null);
     }