Add new features and tests for AirGap and Time modules

- Introduced `SbomService` tasks documentation.
- Updated `StellaOps.sln` to include new projects: `StellaOps.AirGap.Time` and `StellaOps.AirGap.Importer`.
- Added unit tests for `BundleImportPlanner`, `DsseVerifier`, `ImportValidator`, and other components in the `StellaOps.AirGap.Importer.Tests` namespace.
- Implemented `InMemoryBundleRepositories` for testing bundle catalog and item repositories.
- Created `MerkleRootCalculator`, `RootRotationPolicy`, and `TufMetadataValidator` tests.
- Developed `StalenessCalculator` and `TimeAnchorLoader` tests in the `StellaOps.AirGap.Time.Tests` namespace.
- Added `fetch-sbomservice-deps.sh` script for offline dependency fetching.

src/Findings/StellaOps.Findings.Ledger/Observability/LedgerMetrics.cs

@@ -31,11 +31,11 @@ internal static class LedgerMetrics
 
     public static void RecordWriteSuccess(TimeSpan duration, string? tenantId, string? eventType, string? source)
     {
-        var tags = new TagList
+        var tags = new KeyValuePair<string, object?>[]
         {
-            { "tenant", tenantId ?? string.Empty },
-            { "event_type", eventType ?? string.Empty },
-            { "source", source ?? string.Empty }
+            new("tenant", tenantId ?? string.Empty),
+            new("event_type", eventType ?? string.Empty),
+            new("source", source ?? string.Empty)
         };
 
         WriteLatencySeconds.Record(duration.TotalSeconds, tags);
@@ -50,12 +50,12 @@ internal static class LedgerMetrics
         string? policyVersion,
         string? evaluationStatus)
     {
-        var tags = new TagList
+        var tags = new KeyValuePair<string, object?>[]
         {
-            { "tenant", tenantId ?? string.Empty },
-            { "event_type", eventType ?? string.Empty },
-            { "policy_version", policyVersion ?? string.Empty },
-            { "evaluation_status", evaluationStatus ?? string.Empty }
+            new("tenant", tenantId ?? string.Empty),
+            new("event_type", eventType ?? string.Empty),
+            new("policy_version", policyVersion ?? string.Empty),
+            new("evaluation_status", evaluationStatus ?? string.Empty)
         };
 
         ProjectionApplySeconds.Record(duration.TotalSeconds, tags);