Update to sodium 1.0.20.1 to .NET 8

CSSUDII.Sodium.Tests/SecretBoxTest.cs

@@ -0,0 +1,36 @@
+using System.Security.Cryptography;
+using NUnit.Framework;
+using static CSSUDII.Sodium.Interop.Libsodium;
+
+namespace CSSUDII.Sodium.Tests;
+
+[TestFixture]
+public sealed class SecretBoxTest
+{
+    [Test]
+    public unsafe void Test()
+    {
+        var message = RandomNumberGenerator.GetBytes(1024);
+        var cipher = RandomNumberGenerator.GetBytes((int)(1024 + crypto_secretbox_MACBYTES));
+
+        var key = stackalloc byte[(int)crypto_secretbox_KEYBYTES];
+        var nonce = stackalloc byte[(int)crypto_secretbox_NONCEBYTES];
+
+        crypto_secretbox_keygen(key);
+        randombytes_buf(nonce, crypto_secretbox_NONCEBYTES);
+        fixed (byte* mPtr = message)
+        fixed (byte* cPtr = cipher)
+        {
+            crypto_secretbox_easy(cPtr, mPtr, (ulong)message.Length, nonce, key);
+        }
+
+        var decrypted = new byte[message.Length];
+        fixed (byte* dPtr = decrypted)
+        fixed (byte* cPtr = cipher)
+        {
+            crypto_secretbox_open_easy(dPtr, cPtr, (ulong)cipher.Length, nonce, key);
+        }
+
+        Assert.That(decrypted, Is.EquivalentTo(message));
+    }
+}