enhancement: add rows parameter to any function that relies on `GT.fmt()`

[juleswg23]

For example, we could adapt the type signature of gt_plt_bar() to the following:

def gt_plt_bar(
    gt: GT,
    columns: SelectExpr = None,
    rows: int | list[int] | None = None,
    fill: str = "purple",
    bar_height: float = 20,
    height: float = 30,
    width: float = 60,
    stroke_color: str | None = "black",
    show_labels: bool = False,
    label_color: str = "white",
    domain: list[int] | list[float] | None = None,
    keep_columns: bool = False,
) -> GT:

The key addition being rows: int | list[int] | None = None,