[Bug]: Wrong integer type in dolfinx::geometry::impl::is_leaf

Hi,

I think the argument type of `bbox` in the function `dolfinx::geometry::impl::is_leaf`:

https://github.com/FEniCS/dolfinx/blob/5c1c561ff2eee35f081b63bc5a17d85f64bd50cf/cpp/dolfinx/geometry/utils.h#L187-L192

should be `std::array` instead of `std::array` corresponding to the return type of `dolfinx::geometry::BoundingBoxTree::bbox`:

https://github.com/FEniCS/dolfinx/blob/5c1c561ff2eee35f081b63bc5a17d85f64bd50cf/cpp/dolfinx/geometry/BoundingBoxTree.h#L400-L411

I think most compilers did not care about this issue since their types `int` and `std::int32_t` are the same, but in general there's no guarantee for that.
Furthermore, wouldn't it be better making `is_leaf` a (static) function of the class `dolfinx::geometry::BoundingBoxTree`?

Start with cpp/dolfinx/geometry/utils.h around is_leaf and compare its bbox argument with the return type of BoundingBoxTree::bbox in cpp/dolfinx/geometry/BoundingBoxTree.h. Confirm the integer types are consistent, then review whether moving is_leaf into BoundingBoxTree is within scope; the change is done when the API types agree and the relevant geometry code still builds and tests pass.

Written by the indexing model from the issue text.