Add unit tests for RancherHubConnector and various exporters

- Implemented tests for RancherHubConnector to validate fetching documents, handling errors, and managing state.
- Added tests for CsafExporter to ensure deterministic serialization of CSAF documents.
- Created tests for CycloneDX exporters and reconciler to verify correct handling of VEX claims and output structure.
- Developed OpenVEX exporter tests to confirm the generation of canonical OpenVEX documents and statement merging logic.
- Introduced Rust file caching and license scanning functionality, including a cache key structure and hash computation.
- Added sample Cargo.toml and LICENSE files for testing Rust license scanning functionality.

src/Scanner/__Libraries/StellaOps.Scanner.Analyzers.Lang.Rust/Internal/RustFileHashCache.cs

@@ -0,0 +1,45 @@
+using System.Collections.Concurrent;
+using System.Security;
+
+namespace StellaOps.Scanner.Analyzers.Lang.Rust.Internal;
+
+internal static class RustFileHashCache
+{
+    private static readonly ConcurrentDictionary<RustFileCacheKey, string> Sha256Cache = new();
+
+    public static bool TryGetSha256(string path, out string? sha256)
+    {
+        sha256 = null;
+
+        if (!RustFileCacheKey.TryCreate(path, out var key))
+        {
+            return false;
+        }
+
+        try
+        {
+            sha256 = Sha256Cache.GetOrAdd(key, static (_, state) => ComputeSha256(state), path);
+            return !string.IsNullOrEmpty(sha256);
+        }
+        catch (IOException)
+        {
+            return false;
+        }
+        catch (UnauthorizedAccessException)
+        {
+            return false;
+        }
+        catch (SecurityException)
+        {
+            return false;
+        }
+    }
+
+    private static string ComputeSha256(string path)
+    {
+        using var stream = File.Open(path, FileMode.Open, FileAccess.Read, FileShare.Read);
+        using var sha = System.Security.Cryptography.SHA256.Create();
+        var hash = sha.ComputeHash(stream);
+        return Convert.ToHexString(hash).ToLowerInvariant();
+    }
+}