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

@@ -248,7 +248,7 @@ mod tests {
         k: usize,
         test_case: &str,
         limit: Option<usize>,
-        exclude: Vec<Vec<usize>>,
+        should_not_be_decodable: Vec<Vec<usize>>,
     ) {
         for c in shards
             .iter()
@@ -262,7 +262,7 @@ mod tests {
 
             let actual = decode::<F>(s);
 
-            if contains_one_of(&is, &exclude) {
+            if contains_one_of(&is, &should_not_be_decodable) {
                 assert!(
                     actual.is_err(),
                     "should not decode with {:?} {test_case}",