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

@@ -287,7 +287,7 @@ mod tests {
         let test_case = format!("TEST | data: {} bytes, k: {}, n: {}", data.len(), k, n);
 
         let shards = encode::<F>(data, &Matrix::random(k, n, &mut rng))
-            .expect(&format!("could not encode {test_case}"));
+            .unwrap_or_else(|_| panic!("could not encode {test_case}"));
 
         try_all_decoding_combinations(data, &shards, k, &test_case, None, vec![]);
     }
@@ -299,7 +299,7 @@ mod tests {
         let test_case = format!("TEST | data: {} bytes, k: {}, n: {}", data.len(), k, n);
 
         let mut shards = encode::<F>(data, &Matrix::random(k, n, &mut rng))
-            .expect(&format!("could not encode {test_case}"));
+            .unwrap_or_else(|_| panic!("could not encode {test_case}"));
 
         let recoding_steps = [
             vec![2, 4],       // =  n