message: Add comments to round_participation.
diff: @@ -395,8 +395,10 @@ fn round_participation<'a, C: Context>(
  };
  opt_vote.map_or(RoundParticipation::No, |(vh, vote)| {
  if vote.round_exp > r_id.trailing_zeros() {
  + // Round length doesn't divide `r_id`, so the validator was not assigned to that round.
  RoundParticipation::Unassigned
  } else if vote.timestamp < r_id {
  + // The latest vote in or before `r_id` was before `r_id`, so they didn't participate.
  RoundParticipation::No
  } else {
  RoundParticipation::Yes(vh)
  