fix(visualization): update ylim function call for consistency

[PabloCarmona]

Description

Address recent mypy errors on visualization matplotlib module:

mypy --show-error-codes src/
src/aihwkit/utils/visualization.py:635: error: No overload variant of "ylim" matches argument type "list[int]"  [call-overload]
src/aihwkit/utils/visualization.py:635: note: Possible overload variants:
src/aihwkit/utils/visualization.py:635: note:     def ylim() -> tuple[float, float]
src/aihwkit/utils/visualization.py:635: note:     def ylim(bottom: float | tuple[float, float] | None = ..., top: float | None = ..., *, emit: bool = ..., auto: bool | None = ..., ymin: float | None = ..., ymax: float | None = ...) -> tuple[float, float]

Details

Passing -1, 1 as separate float-compatible arguments matches the overload signature ylim(bottom, top). A list[int] technically satisfied the tuple[float, float] variant in older mypy versions via looser checking, but newer mypy is stricter about the distinction between list and tuple.

https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.ylim.html