Add unit tests for SBOM ingestion and transformation

- Implement `SbomIngestServiceCollectionExtensionsTests` to verify the SBOM ingestion pipeline exports snapshots correctly.
- Create `SbomIngestTransformerTests` to ensure the transformation produces expected nodes and edges, including deduplication of license nodes and normalization of timestamps.
- Add `SbomSnapshotExporterTests` to test the export functionality for manifest, adjacency, nodes, and edges.
- Introduce `VexOverlayTransformerTests` to validate the transformation of VEX nodes and edges.
- Set up project file for the test project with necessary dependencies and configurations.
- Include JSON fixture files for testing purposes.

src/Scheduler/__Libraries/StellaOps.Scheduler.Models/Run.cs

@@ -21,6 +21,7 @@ public sealed record Run
         DateTimeOffset? finishedAt = null,
         string? error = null,
         IEnumerable<DeltaSummary>? deltas = null,
+        string? retryOf = null,
         string? schemaVersion = null)
         : this(
             id,
@@ -35,6 +36,7 @@ public sealed record Run
             Validation.NormalizeTimestamp(finishedAt),
             Validation.TrimToNull(error),
             NormalizeDeltas(deltas),
+            Validation.TrimToNull(retryOf),
             schemaVersion)
     {
     }
@@ -53,6 +55,7 @@ public sealed record Run
         DateTimeOffset? finishedAt,
         string? error,
         ImmutableArray<DeltaSummary> deltas,
+        string? retryOf,
         string? schemaVersion = null)
     {
         Id = Validation.EnsureId(id, nameof(id));
@@ -69,6 +72,7 @@ public sealed record Run
         Deltas = deltas.IsDefault
             ? ImmutableArray<DeltaSummary>.Empty
             : deltas.OrderBy(static delta => delta.ImageDigest, StringComparer.Ordinal).ToImmutableArray();
+        RetryOf = Validation.TrimToNull(retryOf);
         SchemaVersion = SchedulerSchemaVersions.EnsureRun(schemaVersion);
     }
 
@@ -103,6 +107,9 @@ public sealed record Run
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
     public ImmutableArray<DeltaSummary> Deltas { get; } = ImmutableArray<DeltaSummary>.Empty;
 
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? RetryOf { get; }
+
     private static ImmutableArray<DeltaSummary> NormalizeDeltas(IEnumerable<DeltaSummary>? deltas)
     {
         if (deltas is null)