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/Findings/StellaOps.Findings.Ledger.WebService/Mappings/LedgerEventMapping.cs

@@ -0,0 +1,72 @@
+using System.Text.Json.Nodes;
+using StellaOps.Findings.Ledger.Domain;
+using StellaOps.Findings.Ledger.WebService.Contracts;
+
+namespace StellaOps.Findings.Ledger.WebService.Mappings;
+
+public static class LedgerEventMapping
+{
+    public static LedgerEventDraft ToDraft(this LedgerEventRequest request)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+
+        var recordedAt = (request.RecordedAt ?? DateTimeOffset.UtcNow).ToUniversalTime();
+        var payload = request.Payload is null ? new JsonObject() : (JsonObject)request.Payload.DeepClone();
+
+        var eventObject = new JsonObject
+        {
+            ["id"] = request.EventId.ToString(),
+            ["type"] = request.EventType,
+            ["tenant"] = request.TenantId,
+            ["chainId"] = request.ChainId.ToString(),
+            ["sequence"] = request.Sequence,
+            ["policyVersion"] = request.PolicyVersion,
+            ["artifactId"] = request.ArtifactId,
+            ["finding"] = new JsonObject
+            {
+                ["id"] = request.Finding.Id,
+                ["artifactId"] = request.Finding.ArtifactId ?? request.ArtifactId,
+                ["vulnId"] = request.Finding.VulnId
+            },
+            ["actor"] = new JsonObject
+            {
+                ["id"] = request.Actor.Id,
+                ["type"] = request.Actor.Type
+            },
+            ["occurredAt"] = FormatTimestamp(request.OccurredAt),
+            ["recordedAt"] = FormatTimestamp(recordedAt),
+            ["payload"] = payload
+        };
+
+        if (request.SourceRunId is Guid sourceRunId && sourceRunId != Guid.Empty)
+        {
+            eventObject["sourceRunId"] = sourceRunId.ToString();
+        }
+
+        var envelope = new JsonObject
+        {
+            ["event"] = eventObject
+        };
+
+        return new LedgerEventDraft(
+            request.TenantId,
+            request.ChainId,
+            request.Sequence,
+            request.EventId,
+            request.EventType,
+            request.PolicyVersion,
+            request.Finding.Id,
+            request.ArtifactId,
+            request.SourceRunId,
+            request.Actor.Id,
+            request.Actor.Type,
+            request.OccurredAt.ToUniversalTime(),
+            recordedAt,
+            payload,
+            envelope,
+            request.PreviousHash);
+    }
+
+    private static string FormatTimestamp(DateTimeOffset value)
+        => value.ToUniversalTime().ToString("yyyy-MM-dd'T'HH:mm:ss.fff'Z'");
+}