message: Remove a TODO; extend finality detector docs.
  Even if we checked that the finality detector is applied to the same
  instance ID as before that doesn't mean it's the same instance of the
  `State` type anyway. Better document it instead.
diff: @@ -26,7 +26,7 @@ pub(crate) struct FttExceeded(Weight);
  /// An incremental finality detector.
  ///
  /// It reuses information between subsequent calls, so it must always be applied to the same
  -/// `State` instance.
  +/// `State` instance: Later calls of `run` must see the same or a superset of the previous state.
  #[derive(Debug)]
  pub(crate) struct FinalityDetector<C: Context> {
  /// The most recent known finalized block.
  @@ -45,7 +45,6 @@ impl<C: Context> FinalityDetector<C> {
  }
  /// Returns all blocks that have been finalized since the last call.
  - // TODO: Verify the consensus instance ID?
  pub(crate) fn run<'a>(
  &'a mut self,
  highway: &'a Highway<C>,
  