working on FEC tests again

• pass n to try_all_decoding_combinations and don't try to decode when shards have been recoded (\#shards > n) and there are no recoded shards in the k combination under review (\max(is) < n)
• pass recoding_steps and should_not_be_decodable as arguments to end_to_end_with_recoding_template
• fix n = 5 => this leads to tests that run in less than 10sec again
• add (k, n) = (8, 10) => tests still run in less than 13sec
• split recoding scenarii into "simple" and "chain"
• show indices in a "pretty" format, i.e. showing indices greater than n as (n), (n + 1), ...

src/fec.rs

@@ -266,7 +266,7 @@ mod tests {
         {
             let is: Vec<usize> = c.iter().map(|(i, _)| *i).collect();
             if there_are_recoded_shards {
-                let contains_recoded_shards = *is.iter().max().unwrap() <= n - 1;
+                let contains_recoded_shards = *is.iter().max().unwrap() < n;
                 if contains_recoded_shards {
                     continue;
                 }
@@ -275,6 +275,7 @@ mod tests {
             let pretty_is = is
                 .iter()
                 .map(|&i| {
+                    #[allow(clippy::comparison_chain)]
                     if i == n {
                         "(n)".into()
                     } else if i > n {