message: Add const qualifier for constructor
diff: @@ -26,7 +26,7 @@ pub struct UnbondingPurse {
  impl UnbondingPurse {
  /// Creates [`UnbondingPurse`] instance for an unbonding request.
  - pub fn new(
  + pub const fn new(
  bonding_purse: URef,
  unbonding_purse: URef,
  validator_public_key: PublicKey,
  