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/__Libraries/StellaOps.Canonical.Json/CanonJson.cs

@@ -1,4 +1,5 @@
 using System.Security.Cryptography;
+using System.Text;
 using System.Text.Json;
 
 namespace StellaOps.Canonical.Json;
@@ -18,6 +19,33 @@ namespace StellaOps.Canonical.Json;
 /// </remarks>
 public static class CanonJson
 {
+    /// <summary>
+    /// Serializes an object to a canonical JSON string.
+    /// Object keys are recursively sorted using Ordinal comparison.
+    /// </summary>
+    /// <typeparam name="T">The type to serialize.</typeparam>
+    /// <param name="obj">The object to serialize.</param>
+    /// <returns>Canonical JSON string.</returns>
+    public static string Serialize<T>(T obj)
+    {
+        var bytes = Canonicalize(obj);
+        return Encoding.UTF8.GetString(bytes);
+    }
+
+    /// <summary>
+    /// Serializes an object to a canonical JSON string using custom serializer options.
+    /// Object keys are recursively sorted using Ordinal comparison.
+    /// </summary>
+    /// <typeparam name="T">The type to serialize.</typeparam>
+    /// <param name="obj">The object to serialize.</param>
+    /// <param name="options">JSON serializer options to use for initial serialization.</param>
+    /// <returns>Canonical JSON string.</returns>
+    public static string Serialize<T>(T obj, JsonSerializerOptions options)
+    {
+        var bytes = Canonicalize(obj, options);
+        return Encoding.UTF8.GetString(bytes);
+    }
+
     /// <summary>
     /// Canonicalizes an object to a deterministic byte array.
     /// Object keys are recursively sorted using Ordinal comparison.