`DTriangle` accessors may read out of bounds in affected versions

In affected versions, `DTriangle::neighbor_by_order` and `DTriangle::vertex_by_order` were public safe functions that accepted an
arbitrary `order` value. These functions used `order` to access fixed-size internal arrays with `get_unchecked`, without checking whether `order` was within bounds. Calling these methods with an out-of-bounds `order` could cause an out-of-bounds read from safe Rust code. This made the old APIs unsound, since safe callers could trigger undefined behavior without using `unsafe`.

The issue was fixed in version `0.29.0` as part of a broader rewrite that replaced the old triangle implementation with `IntTriangle` and removed the affected accessor methods.