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.

tests/AirGap/StellaOps.AirGap.Time.Tests/TimeStatusDtoTests.cs

@@ -0,0 +1,20 @@
+using StellaOps.AirGap.Time.Models;
+
+namespace StellaOps.AirGap.Time.Tests;
+
+public class TimeStatusDtoTests
+{
+    [Fact]
+    public void SerializesDeterministically()
+    {
+        var status = new TimeStatus(
+            new TimeAnchor(DateTimeOffset.Parse("2025-01-01T00:00:00Z"), "source", "fmt", "fp", "digest"),
+            new StalenessEvaluation(42, 10, 20, true, false),
+            new StalenessBudget(10, 20),
+            DateTimeOffset.Parse("2025-01-02T00:00:00Z"));
+
+        var json = TimeStatusDto.FromStatus(status).ToJson();
+
+        Assert.Equal("{\"anchorTime\":\"2025-01-01T00:00:00.0000000Z\",\"format\":\"fmt\",\"source\":\"source\",\"fingerprint\":\"fp\",\"digest\":\"digest\",\"ageSeconds\":42,\"warningSeconds\":10,\"breachSeconds\":20,\"isWarning\":true,\"isBreach\":false,\"evaluatedAtUtc\":\"2025-01-02T00:00:00.0000000Z\"}", json);
+    }
+}