Add support for event balance_update.

bfxapi/websocket/_handlers/auth_events_handler.py

@@ -34,6 +34,7 @@ class AuthEventsHandler:
         "ws": "wallet_snapshot",
         "wu": "wallet_update",
         "fiu": "funding_info_update",
+        "bu": "balance_update",
     }
 
     __SERIALIZERS: Dict[Tuple[str, ...], serializers._Serializer] = {
@@ -45,6 +46,7 @@ class AuthEventsHandler:
         ("fls", "fln", "flu", "flc"): serializers.FundingLoan,
         ("ws", "wu"): serializers.Wallet,
         ("fiu",): serializers.FundingInfo,
+        ("bu",): serializers.BalanceInfo,
     }
 
     def __init__(self, event_emitter: EventEmitter) -> None: