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

add "unchecked" versions of `Matrix::{vandermonde,from_vec_vec}` and test both matrices (dragoon/komodo!75)

## 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