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/StellaOps.Scheduler.WebService/SchedulerEndpointHelpers.cs

@@ -1,7 +1,9 @@
-using System.ComponentModel.DataAnnotations;
-using System.Globalization;
-using StellaOps.Scheduler.Models;
-using StellaOps.Scheduler.Storage.Mongo.Services;
+using System.ComponentModel.DataAnnotations;
+using System.Globalization;
+using System.Text;
+using StellaOps.Scheduler.Models;
+using StellaOps.Scheduler.Storage.Mongo.Repositories;
+using StellaOps.Scheduler.Storage.Mongo.Services;
 
 namespace StellaOps.Scheduler.WebService;
 
@@ -91,11 +93,11 @@ internal static class SchedulerEndpointHelpers
         return null;
     }
 
-    public static DateTimeOffset? TryParseDateTimeOffset(string? value)
-    {
-        if (string.IsNullOrWhiteSpace(value))
-        {
-            return null;
+    public static DateTimeOffset? TryParseDateTimeOffset(string? value)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            return null;
         }
 
         if (DateTimeOffset.TryParse(value, CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out var parsed))
@@ -114,14 +116,62 @@ internal static class SchedulerEndpointHelpers
             throw new ArgumentException("Tenant identifier must be provided.", nameof(tenantId));
         }
 
-        return new Selector(
-            selection.Scope,
-            tenantId,
-            selection.Namespaces,
-            selection.Repositories,
-            selection.Digests,
-            selection.IncludeTags,
-            selection.Labels,
-            selection.ResolvesTags);
-    }
-}
+        return new Selector(
+            selection.Scope,
+            tenantId,
+            selection.Namespaces,
+            selection.Repositories,
+            selection.Digests,
+            selection.IncludeTags,
+            selection.Labels,
+            selection.ResolvesTags);
+    }
+
+    public static string CreateRunCursor(Run run)
+    {
+        ArgumentNullException.ThrowIfNull(run);
+        var payload = $"{run.CreatedAt.ToUniversalTime():O}|{run.Id}";
+        return Convert.ToBase64String(Encoding.UTF8.GetBytes(payload));
+    }
+
+    public static RunListCursor? TryParseRunCursor(string? value)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            return null;
+        }
+
+        var trimmed = value.Trim();
+        if (trimmed.Length == 0)
+        {
+            return null;
+        }
+
+        try
+        {
+            var bytes = Convert.FromBase64String(trimmed);
+            var decoded = Encoding.UTF8.GetString(bytes);
+            var parts = decoded.Split('|', 2, StringSplitOptions.TrimEntries);
+            if (parts.Length != 2)
+            {
+                throw new ValidationException($"Cursor '{value}' is not valid.");
+            }
+
+            if (!DateTimeOffset.TryParse(parts[0], CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out var timestamp))
+            {
+                throw new ValidationException($"Cursor '{value}' is not valid.");
+            }
+
+            if (string.IsNullOrWhiteSpace(parts[1]))
+            {
+                throw new ValidationException($"Cursor '{value}' is not valid.");
+            }
+
+            return new RunListCursor(timestamp.ToUniversalTime(), parts[1]);
+        }
+        catch (FormatException ex)
+        {
+            throw new ValidationException($"Cursor '{value}' is not valid.", ex);
+        }
+    }
+}