Feat: add npm golden vector decode test

Co-authored-by: gpt-5.3-codex <no-reply@openai.com>

tests/zwus.rs

@@ -26,3 +26,35 @@ fn decode_ignores_non_zwus_characters() {
     let mixed = format!("te{hidden}xt");
     assert_eq!(Zwus::decode_to_string_with_base(&mixed, 6), "secret");
 }
+
+#[test]
+fn npm_vectors_decode_to_test123_checkmark() {
+    // Paste encoded outputs from your npm package here:
+    //   zwus.encodeString("Test123!✅", 3)
+    //   zwus.encodeString("Test123!✅", 6)
+    //   zwus.encodeString("Test123!✅", 8)
+    //
+    // Keep these as raw strings to preserve invisible chars exactly.
+    let npm_base_3 = r#""#;
+    let npm_base_6 = r#""#;
+    let npm_base_8 = r#""#;
+
+    let expected = "Test123!✅";
+
+    assert!(
+        !npm_base_3.is_empty(),
+        "Paste base-3 encoded payload into npm_base_3"
+    );
+    assert!(
+        !npm_base_6.is_empty(),
+        "Paste base-6 encoded payload into npm_base_6"
+    );
+    assert!(
+        !npm_base_8.is_empty(),
+        "Paste base-8 encoded payload into npm_base_8"
+    );
+
+    assert_eq!(Zwus::decode_to_string_with_base(npm_base_3, 3), expected);
+    assert_eq!(Zwus::decode_to_string_with_base(npm_base_6, 6), expected);
+    assert_eq!(Zwus::decode_to_string_with_base(npm_base_8, 8), expected);
+}