…oft#572)

The 1.6.0 signature

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

regressed type-checking for callers passing a more precise
list type such as list[tuple[str, str, str, str, int, str]].
Because typing.List is invariant, mypy rejects it with:

    error: Argument 2 to "executemany" of "Cursor" has
    incompatible type "list[tuple[...]]"; expected
    "list[Sequence[Any]] | list[Mapping[str, Any]]"  [arg-type]
    note: "list" is invariant -- see ...
    note: Consider using "Sequence" instead, which is covariant

In 1.5.0 the parameter was a single arm (List[Sequence[Any]])
which mypy accepted via the gradual-typing escape hatch on Any;
the union introduced in 1.6.0 forces mypy to pick a matching arm
and invariance kicks in, breaking previously valid call sites.

Switch to the covariant Sequence outer container on both the
public Cursor.executemany and the internal
_transpose_rowwise_to_columnwise helper:

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

This:
- accepts list[tuple[...]], list[list[...]], tuple of tuples, etc.;
- matches PEP 249 ("sequence of sequences");
- aligns with pyodbc's typing;
- keeps the 1.6.0 dict/pyformat support intact.

Runtime behaviour is unchanged.

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

Two follow-ups from the Copilot PR review on microsoft#586:

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 misleading - the
   transpose loop would yield mapping keys, not values. Narrow its
   annotation to Sequence[Sequence[Any]] only.

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