message: Move weight boundaries checks to `build()` method.
diff: @@ -636,8 +636,6 @@ impl<C: Context<ValidatorId = ValidatorId>, DS: DeliveryStrategy<C>>
  }
  pub(crate) fn weight_limits(mut self, lower: u64, upper: u64) -> Self {
  - // TODO: More checks?
  - assert!(lower <= upper);
  self.weight_limits = (lower, upper);
  self
  }
  @@ -696,6 +694,16 @@ impl<C: Context<ValidatorId = ValidatorId>, DS: DeliveryStrategy<C>>
  let round_exp = self.round_exp;
  let start_time = self.start_time;
  + let (lower, upper) = if self.weight_limits == (0, 0) {
  + return Err(BuilderError::WeightLimits);
  + } else {
  + let (l, u) = self.weight_limits;
  + if (l >= u) {
  + return Err(BuilderError::WeightLimits);
  + }
  + (l, u)
  + };
  +
  let weights: Vec<Weight> = match self.weight_distribution {
  Distribution::Constant => {
  let (lower, upper) = self.weight_limits;
  