Implement Exception Effect Registry and Evaluation Service

- Added IExceptionEffectRegistry interface and its implementation ExceptionEffectRegistry to manage exception effects based on type and reason.
- Created ExceptionAwareEvaluationService for evaluating policies with automatic exception loading from the repository.
- Developed unit tests for ExceptionAdapter and ExceptionEffectRegistry to ensure correct behavior and mappings of exceptions and effects.
- Enhanced exception loading logic to filter expired and non-active exceptions, and to respect maximum exceptions limit.
- Implemented caching mechanism in ExceptionAdapter to optimize repeated exception loading.

src/Policy/StellaOps.Policy.Engine/Telemetry/PolicyEngineTelemetry.cs

@@ -469,6 +469,20 @@ public static class PolicyEngineTelemetry
             unit: "events",
             description: "Lifecycle events for exceptions (activated, expired, revoked).");
 
+    // Counter: policy_exception_loaded_total{tenant}
+    private static readonly Counter<long> ExceptionLoadedCounter =
+        Meter.CreateCounter<long>(
+            "policy_exception_loaded_total",
+            unit: "exceptions",
+            description: "Total exceptions loaded from repository for evaluation.");
+
+    // Histogram: policy_exception_load_latency_seconds{tenant}
+    private static readonly Histogram<double> ExceptionLoadLatencyHistogram =
+        Meter.CreateHistogram<double>(
+            "policy_exception_load_latency_seconds",
+            unit: "s",
+            description: "Latency of loading exceptions from repository.");
+
     /// <summary>
     /// Counter for exception cache operations.
     /// </summary>
@@ -879,6 +893,23 @@ public static class PolicyEngineTelemetry
         ExceptionLifecycleCounter.Add(1, tags);
     }
 
+    /// <summary>
+    /// Records exceptions loaded from repository for evaluation.
+    /// </summary>
+    /// <param name="tenant">Tenant identifier.</param>
+    /// <param name="count">Number of exceptions loaded.</param>
+    /// <param name="latencySeconds">Time taken to load exceptions in seconds.</param>
+    public static void RecordExceptionLoaded(string tenant, int count, double latencySeconds)
+    {
+        var tags = new TagList
+        {
+            { "tenant", NormalizeTenant(tenant) },
+        };
+
+        ExceptionLoadedCounter.Add(count, tags);
+        ExceptionLoadLatencyHistogram.Record(latencySeconds, tags);
+    }
+
     #region Golden Signals - Recording Methods
 
     /// <summary>