Add specialized point in triangle test

[Huite]

This might be worthwhile when dealing with a fully triangular grid.

Coming from xugrid:

@nb.njit(inline="always")
def point_in_triangle(p: Point, triangle: Triangle) -> bool:
    """Unrolled half-plane check."""
    a = cross_product(to_vector(triangle.a, triangle.b), to_vector(triangle.a, p)) > 0
    b = cross_product(to_vector(triangle.b, triangle.c), to_vector(triangle.b, p)) > 0
    c = cross_product(to_vector(triangle.c, triangle.a), to_vector(triangle.c, p)) > 0
    return (a == b) and (b == c)

@nb.njit(inline="always", parallel=True, cache=True)
def points_in_triangles(
    points: FloatArray,
    face_indices: IntArray,
    faces: IntArray,
    vertices: FloatArray,
):
    n_points = len(points)
    inside = np.empty(n_points, dtype=np.bool_)
    for i in nb.prange(n_points):
        face_index = face_indices[i]
        face = faces[face_index]
        triangle = as_triangle(vertices, face)
        point = as_point(points[i])
        inside[i] = point_in_triangle(point, triangle)
    return inside