add "unchecked" versions of `Matrix::{vandermonde,from_vec_vec}` and test both matrices

changelog

• replace Matrix::vandermonde with Matrix::vandermonde_unchecked
• add a new Matrix::vandermonde which calls Matrix::vandermonde_unchecked after checking the seed points are distinct, otherwise, gives a KomodoError::InvalidVandermonde error
• same with Matrix::from_vec_vec and Matrix::from_vec_vec_unchecked
• add documentation tests for the two "checked" functions
• run the main lib tests on both a random and a Vandermond matrix, just to be sure we do not take advantage of the Vandermonde structure