MOD: Make end optional in C++ client

Author: threecgreen

databento/historical/api/batch.py

@@ -55,7 +55,7 @@ def __init__(self, key: str, gateway: str) -> None:
     def submit_job(
         self,
         dataset: Union[Dataset, str],
-        symbols: Optional[Union[List[str], str]],
+        symbols: Union[List[str], str],
         schema: Union[Schema, str],
         start: Union[pd.Timestamp, date, str, int],
         end: Optional[Union[pd.Timestamp, date, str, int]] = None,