fix: add-type-hints-transaction-sign (hiero-ledger#1649)

Signed-off-by: Parth J Chaudhary <[email protected]>

Author: Pikolosan

CHANGELOG.md

@@ -136,6 +136,7 @@ This changelog is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.
 - Added comprehensive docstring to `compress_with_cryptography` function (#1626)
 
 ### Changed
+- Added missing type hints to sign method in Transaction class (#1630)
 - Refactored `examples/consensus/topic_create_transaction.py` to use `Client.from_env()` (#1611)
 - Updated GitHub Actions setup-node action to v6.2.0.
 - chore: format tests/unit/mock_server.py with black (#1542)

src/hiero_sdk_python/transaction/transaction.py

@@ -18,6 +18,7 @@
 from hiero_sdk_python.utils.key_utils import Key, key_to_proto
 
 if TYPE_CHECKING:
+    from hiero_sdk_python.crypto.private_key import PrivateKey
     from hiero_sdk_python.schedule.schedule_create_transaction import (
         ScheduleCreateTransaction,
     )
@@ -165,7 +166,7 @@ def _map_status_error(self, response):
 
         return PrecheckError(error_code, tx_id)
 
-    def sign(self, private_key):
+    def sign(self, private_key: "PrivateKey") -> "Transaction":
         """
         Signs the transaction using the provided private key.