Add OP_RETURN support for heirs

Allow heirs to produce an OP_RETURN output instead of a regular BTC
payment. An address prefixed with OP_RETURN: carries hex data (max 80
bytes); such heirs always have amount 0 and are excluded from amount
calculations. GUI dialog shows a message field with the decoded text,
the heir list displays the decoded message, and the OP_RETURN output
is emitted with zero value in inheritance transactions.

tests/test_core_heirs.py

@@ -16,7 +16,9 @@ sys.path.insert(0, os.path.join(os.path.dirname(__file__), os.pardir))
 from bal.core.heirs import (
     HEIR_ADDRESS, HEIR_AMOUNT, HEIR_LOCKTIME, HEIR_REAL_AMOUNT,
     HEIR_DUST_AMOUNT, TRANSACTION_LABEL,
+    OP_RETURN_PREFIX,
     create_op_return_script,
+    is_op_return_address, get_op_return_hex, validate_op_return_hex,
     AliasNotFoundException,
     NotAnAddress, AmountNotValid, LocktimeNotValid,
     HeirExpiredException, HeirAmountIsDustException,
@@ -258,6 +260,96 @@ def test_validate_removes_invalid():
     assert "alice" in result or True  # may or may not pass address check
 
 
+# ------------------------------------------------------------------ #
+# OP_RETURN helpers
+# ------------------------------------------------------------------ #
+
+def test_op_return_prefix_constant():
+    assert OP_RETURN_PREFIX == "OP_RETURN:"
+
+
+def test_is_op_return_address():
+    assert is_op_return_address("OP_RETURN:48656c6c6f")
+    assert not is_op_return_address("bc1qar0srrr7xfkvy5l643lydnw9re59gtzzwf5mdq")
+    assert not is_op_return_address("")
+    assert not is_op_return_address("OP_RETURN")
+    assert not is_op_return_address("OP_RETURNX:")
+
+
+def test_get_op_return_hex():
+    assert get_op_return_hex("OP_RETURN:48656c6c6f") == "48656c6c6f"
+    assert get_op_return_hex("bc1q...") is None
+    assert get_op_return_hex("") is None
+
+
+def test_validate_op_return_hex_valid():
+    validate_op_return_hex("48656c6c6f")
+
+
+def test_validate_op_return_hex_invalid():
+    try:
+        validate_op_return_hex("nothex!!")
+        assert False, "expected NotAnAddress"
+    except NotAnAddress:
+        pass
+
+
+def test_validate_op_return_hex_too_long():
+    try:
+        validate_op_return_hex("ab" * 81)
+        assert False, "expected NotAnAddress"
+    except NotAnAddress:
+        pass
+
+
+def test_validate_op_return_hex_empty():
+    validate_op_return_hex("")
+
+
+def test_validate_address_op_return():
+    addr = "OP_RETURN:48656c6c6f"
+    result = Heirs.validate_address(addr)
+    assert result == addr
+
+
+def test_validate_heir_op_return():
+    k = "test_op_return"
+    v = ["OP_RETURN:48656c6c6f", "0", "30d"]
+    result = Heirs.validate_heir(k, v)
+    assert result[0] == "OP_RETURN:48656c6c6f"
+    assert result[1] == "0"
+
+
+# ------------------------------------------------------------------ #
+# Heirs class OP_RETURN integration
+# ------------------------------------------------------------------ #
+
+def test_heirs_fixed_percent_skips_op_return():
+    class FakeWallet:
+        class FakeDB:
+            def __init__(self):
+                self._data = {}
+            def get(self, key, default=None):
+                return self._data.get(key, default)
+            def put(self, key, value):
+                self._data[key] = value
+        def __init__(self):
+            self.db = self.FakeDB()
+            self.dust_threshold = lambda: 500
+    wallet = FakeWallet()
+    heirs = Heirs(wallet)
+    heirs["op_ret"] = ["OP_RETURN:48656c6c6f", "0", "9999999999"]
+    heirs["normal"] = ["addr1", "10000", "9999999999"]
+    fixed_h, fixed_amt, perc_h, perc_amt, fixed_with_dust = (
+        heirs.fixed_percent_lists_amount(0, 500)
+    )
+    assert "op_ret" in fixed_h
+    assert "normal" in fixed_h
+    assert fixed_h["op_ret"][HEIR_REAL_AMOUNT] == 0
+    assert fixed_h["normal"][HEIR_REAL_AMOUNT] == 10000
+    assert fixed_amt == 10000  # OP_RETURN adds 0
+
+
 if __name__ == "__main__":
     for name in sorted(dir()):
         if name.startswith("test_"):