complete the FEC and "linear algebra" tests

• komodo::linalg::Matrix::random is tested
• komodo::linalg::Matrix::inverse is tested on more matrix sizes, from 1 to 20 random matrices
• komodo::field tests have been double-checked
• pure "recoding" tests from komodo::fec have been double-checked
• end_to_end and end_to_end_with_recoding now runs for k \in [3, 5] and \rho \in [\frac{1}{2}, \frac{1}{3}] with n = \lfloor \frac{k}{\rho} \rfloor
• all "k among n + t" combinations are tested with try_all_decoding_combinations, possibly with some removals in case recoding is involved with is_inside

Important
on my machine, make test goes from less than 8sec on latest main to around 40sec with this MR

src/fec.rs

@@ -217,6 +217,10 @@ mod tests {
         F::from_le_bytes_mod_order(&n.to_le_bytes())
     }
 
+    /// `is_inside(set, x)` is true iif `x` fully contains one of the lists from `set`
+    ///
+    /// > **Note**  
+    /// > see [`exclusion`] for some example
     fn is_inside(set: &[Vec<usize>], x: &[usize]) -> bool {
         set.iter().any(|y| y.iter().all(|z| x.contains(z)))
     }