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.

tools/offline/fetch-sbomservice-deps.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")/../.." && pwd)"
+PACKAGES_DIR="$ROOT/local-nugets/packages"
+TMP_DIR="$ROOT/tmp/sbomservice-feed"
+PROJECT="$TMP_DIR/probe.csproj"
+
+mkdir -p "$TMP_DIR" "$PACKAGES_DIR"
+
+cat > "$PROJECT" <<'CS'
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.IdentityModel.Tokens" Version="8.14.0" />
+    <PackageReference Include="Pkcs11Interop" Version="4.1.0" />
+  </ItemGroup>
+</Project>
+CS
+
+dotnet restore "$PROJECT" \
+  --packages "$PACKAGES_DIR" \
+  --ignore-failed-sources \
+  /p:RestoreUseStaticGraphEvaluation=true \
+  /p:RestorePackagesWithLockFile=false
+
+find "$PACKAGES_DIR" -name '*.nupkg' -maxdepth 5 -type f -printf '%P\n' | sort