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/AirGap/StellaOps.AirGap.Time/Models/TimeStatus.cs

@@ -0,0 +1,10 @@
+namespace StellaOps.AirGap.Time.Models;
+
+public sealed record TimeStatus(
+    TimeAnchor Anchor,
+    StalenessEvaluation Staleness,
+    StalenessBudget Budget,
+    DateTimeOffset EvaluatedAtUtc)
+{
+    public static TimeStatus Empty => new(TimeAnchor.Unknown, StalenessEvaluation.Unknown, StalenessBudget.Default, DateTimeOffset.UnixEpoch);
+}