Pass Span instead of Memory

IdentityShroud.TestUtils/Substitutes/NullDekEncryptionService.cs

@@ -0,0 +1,18 @@
+using IdentityShroud.Core.Contracts;
+using IdentityShroud.Core.Security;
+
+namespace IdentityShroud.TestUtils.Substitutes;
+
+public class NullDekEncryptionService : IDekEncryptionService
+{
+    public KekId KeyId { get; } = KekId.NewId(); 
+    public EncryptedDek Encrypt(ReadOnlySpan<byte> plain)
+    {
+        return new(KeyId, plain.ToArray());
+    }
+
+    public byte[] Decrypt(EncryptedDek input)
+    {
+        return input.Value;
+    }
+}