Fix invisible narrow bins and incorrect extreme-value counts

[ElouenGinat]

Bugs

• Very narrow adaptive bins can be invisible unless callers set an explicit edge color.
• khisto.matplotlib.hist lets Matplotlib recount samples, so extreme finite values can produce counts or densities that differ from khisto.histogram.

Expected

Keep narrow bins visible by default while preserving explicit edge styles, and plot Khiops frequencies directly so both APIs return identical values.