working on the rank algorithm

tries to address #5 (closed)

changelog

• the rank.rs example now only returns the rank to stdout
• two tests have been added
  • one that asserts \text{r}(M^T) = \text{r}(M)
  • one that asserts \text{r}(M) \leq \min(n, m) when n and m are the heigth and the width of M respectively
• Matrix::rank has been rewritten thanks to ChatGPT, the full prompt can be found in the body of 384d9559 and the algorithm has been refactored and simplified in the following few commits

Note
the two new tests do not pass on e27561bb but do pass on the tip of this MR branch, which indicates that the bugs have been solved