Implement ledger metrics for observability and add tests for Ruby packages endpoints

- Added `LedgerMetrics` class to record write latency and total events for ledger operations.
- Created comprehensive tests for Ruby packages endpoints, covering scenarios for missing inventory, successful retrieval, and identifier handling.
- Introduced `TestSurfaceSecretsScope` for managing environment variables during tests.
- Developed `ProvenanceMongoExtensions` for attaching DSSE provenance and trust information to event documents.
- Implemented `EventProvenanceWriter` and `EventWriter` classes for managing event provenance in MongoDB.
- Established MongoDB indexes for efficient querying of events based on provenance and trust.
- Added models and JSON parsing logic for DSSE provenance and trust information.

src/Concelier/__Tests/StellaOps.Concelier.WebService.Tests/AdvisoryAiTelemetryTests.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics.Metrics;
-using FluentAssertions;
 using Microsoft.Extensions.Logging.Abstractions;
 using StellaOps.Concelier.WebService.Services;
 using StellaOps.Concelier.WebService.Diagnostics;
@@ -12,7 +11,7 @@ namespace StellaOps.Concelier.WebService.Tests;
 public sealed class AdvisoryAiTelemetryTests : IDisposable
 {
     private readonly MeterListener _listener;
-    private readonly List<Measurement<long>> _guardrailMeasurements = new();
+    private readonly List<(long Value, KeyValuePair<string, object?>[] Tags)> _guardrailMeasurements = new();
 
     public AdvisoryAiTelemetryTests()
     {
@@ -31,7 +30,7 @@ public sealed class AdvisoryAiTelemetryTests : IDisposable
             if (instrument.Meter.Name == AdvisoryAiMetrics.MeterName &&
                 instrument.Name == "advisory_ai_guardrail_blocks_total")
             {
-                _guardrailMeasurements.Add(new Measurement<long>(measurement, tags, state));
+                _guardrailMeasurements.Add((measurement, tags.ToArray()));
             }
         });
         _listener.Start();
@@ -58,10 +57,20 @@ public sealed class AdvisoryAiTelemetryTests : IDisposable
             Duration: TimeSpan.FromMilliseconds(5),
             GuardrailCounts: guardrailCounts));
 
-        _guardrailMeasurements.Should().ContainSingle();
-        var measurement = _guardrailMeasurements[0];
-        measurement.Value.Should().Be(2);
-        measurement.Tags.Should().Contain(tag => tag.Key == "cache" && (string?)tag.Value == "hit");
+        var measurement = Assert.Single(_guardrailMeasurements);
+        Assert.Equal(2, measurement.Value);
+
+        var cacheHitTagFound = false;
+        foreach (var tag in measurement.Tags)
+        {
+            if (tag.Key == "cache" && (string?)tag.Value == "hit")
+            {
+                cacheHitTagFound = true;
+                break;
+            }
+        }
+
+        Assert.True(cacheHitTagFound, "guardrail measurement should be tagged with cache hit outcome.");
     }
 
     public void Dispose()