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/Cli/StellaOps.Cli/Services/BackendOperationsClient.cs

@@ -901,7 +901,8 @@ internal sealed class BackendOperationsClient : IBackendOperationsClient
             throw new ArgumentException("Scan identifier is required.", nameof(scanId));
         }
 
-        using var request = CreateRequest(HttpMethod.Get, $"api/scans/{scanId}/ruby-packages");
+        var encodedScanId = Uri.EscapeDataString(scanId);
+        using var request = CreateRequest(HttpMethod.Get, $"api/scans/{encodedScanId}/ruby-packages");
         await AuthorizeRequestAsync(request, cancellationToken).ConfigureAwait(false);
 
         using var response = await _httpClient.SendAsync(request, cancellationToken).ConfigureAwait(false);