feat(observability): meter bounded API-key store lookups

src/Server/ZB.MOM.WW.OtOpcUa.Host/OpcUa/BoundedApiKeyStore.cs

@@ -1,6 +1,7 @@
 using System.Collections.Concurrent;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
+using ZB.MOM.WW.OtOpcUa.Commons.Observability;
 using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
 using ZB.MOM.WW.OtOpcUa.Core.Authorization;
 
@@ -139,6 +140,8 @@ public sealed class BoundedApiKeyStore : IApiKeyStore
     {
         if (cache.TryGetValue(key, out var entry) && _time.GetUtcNow() - entry.StampedUtc < ttl)
         {
+            OtOpcUaTelemetry.ApiKeyStoreBounded.Add(
+                1, new KeyValuePair<string, object?>("outcome", "cache_hit"));
             value = entry.Value;
             return true;
         }
@@ -202,6 +205,8 @@ public sealed class BoundedApiKeyStore : IApiKeyStore
         }
         catch (OperationCanceledException) when (!ct.IsCancellationRequested)
         {
+            OtOpcUaTelemetry.ApiKeyStoreBounded.Add(
+                1, new KeyValuePair<string, object?>("outcome", "timeout"));
             _log.LogWarning(
                 "ApiKeyStore: the key store did not answer within {TimeoutMs} ms — denying this activation. "
                 + "Every OPC UA session activation on this server is serialized behind this call; "