feat: add HD wallet generator with BIP-44/49/84/86 support

- Add src/hd_wallet.py with deterministic key derivation (BIP-32/39)
- Support P2PKH (BIP-44), P2SH-P2WPKH (BIP-49), P2WPKH (BIP-84), P2TR (BIP-86)
- JSON output aligned to Electrum wallet format (keystore, xpub/xprv, derivation path, root fingerprint)
- Add tests/test_hd_wallet.py with 34 tests (structure, prefixes, determinism, SecretScan)
- Add bip-utils to requirements.txt
- Add option 6 to __main__.py menu

__main__.py

@@ -9,15 +9,17 @@ def main():
     print("3. P2SH")
     print("4. P2WPKH")
     print("5. P2TR")
-    
+    print("6. HD Wallet (BIP-44/49/84/86)")
+
     choice = input("Inserisci la tua scelta: ").strip()
-    
+
     scripts = {
         '1': 'src/p2pk.py',
         '2': 'src/p2pkh.py',
         '3': 'src/p2sh.py',
         '4': 'src/p2wpkh.py',
-        '5': 'src/p2tr.py'
+        '5': 'src/p2tr.py',
+        '6': 'src/hd_wallet.py',
     }
     
     if choice in scripts: