Add tests for SBOM generation determinism across multiple formats

- Created `StellaOps.TestKit.Tests` project for unit tests related to determinism.
- Implemented `DeterminismManifestTests` to validate deterministic output for canonical bytes and strings, file read/write operations, and error handling for invalid schema versions.
- Added `SbomDeterminismTests` to ensure identical inputs produce consistent SBOMs across SPDX 3.0.1 and CycloneDX 1.6/1.7 formats, including parallel execution tests.
- Updated project references in `StellaOps.Integration.Determinism` to include the new determinism testing library.

src/Scheduler/__Tests/StellaOps.Scheduler.ImpactIndex.Tests/RoaringImpactIndexTests.cs

@@ -231,6 +231,7 @@ public sealed class RoaringImpactIndexTests
         await index.RemoveAsync(digest1);
 
         var snapshot = await index.CreateSnapshotAsync();
+        snapshot.SnapshotId.Should().MatchRegex("^snap-[0-9a-f]{64}$");
 
         var restored = new RoaringImpactIndex(NullLogger<RoaringImpactIndex>.Instance);
         await restored.RestoreSnapshotAsync(snapshot);