feat: implement Argon2 algorithm

tests/test_algorithms.py

@@ -38,3 +38,17 @@ def test_pbkdf2_algorithm_respects_iterations():
     salt2, hash2 = algo.hash("test", iterations=200000)
     # Different iterations should produce different hashes even with same password
     assert hash1 != hash2
+
+
+def test_argon2_algorithm_hash_round_trip():
+    """Verify Argon2 algorithm can hash and verify passwords."""
+    algo = get_algorithm("argon2")
+    salt, hashed = algo.hash("test password")
+    assert algo.verify("test password", salt, hashed)
+    assert not algo.verify("wrong password", salt, hashed)
+
+
+def test_argon2_algorithm_identifier():
+    """Verify Argon2 algorithm has correct identifier."""
+    algo = get_algorithm("argon2")
+    assert algo.identifier == "argon2"