FIX: Address Copilot review on # sync .pyi stub, narrow internal helper586

Two follow-ups from the Copilot PR review:

1. mssql_python/mssql_python.pyi still carried the old invariant
   signature

       seq_of_parameters: Union[List[Sequence[Any]], List[Mapping[str, Any]]]

   Sync it to the covariant Sequence form to match cursor.py and
   prevent a silent regression if the stub is ever relocated to
   __init__.pyi (where mypy would actually consume it).

2. _transpose_rowwise_to_columnwise is only ever called with
   already-converted positional rows (pyformat-to-qmark conversion
   happens upstream in executemany before transposition). Advertising
   it as accepting Mapping rows is  the transpose loopmisleading
   would yield mapping keys, not values. Narrow its annotation to
   Sequence[Sequence[Any]] only.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bewithgaurav

mssql_python/cursor.py

@@ -2015,7 +2015,7 @@ def columns(self, table=None, catalog=None, schema=None, column=None):
 
     def _transpose_rowwise_to_columnwise(
         self,
-        seq_of_parameters: Union[Sequence[Sequence[Any]], Sequence[Mapping[str, Any]]],
+        seq_of_parameters: Sequence[Sequence[Any]],
     ) -> tuple[list, int]:
         """
         Convert sequence of rows (row-wise) into list of columns (column-wise),