Shared numeric array type aliases (VecN, MatN) used across trendify.plotting/
trendify.styling for fields like Trace2D.x/Trace2D.y and HistogramStyle.bins. Backed by
numpydantic.NDArray for runtime pydantic validation, with a plain TypeAlias swapped in under
TYPE_CHECKING so static type checkers see an ordinary array/list/tuple union instead of
numpydantic's shape-annotated generic.