Rounding bugs: `LUP` calculated index inconsistency; `t0debtInAuction` accumulator in inconsistent state

[grandizzy]

Description of change

High level

• Issue 1: LUP index calculated in PoolUtils can differ from the Pool calculated LUP index, due to inconsistent roundings

  • This could happen because in Pool.debtInfo function which is used by PoolUtils the pool debt is always rounded up by using ceilWmul while in Pool._accruePoolInterest it is rounded to nearest (by using plain wmul). Hence the invariant logic in attached regression test was not applying the add quote token under LUP penalty while pool did, resulting in inconsistent deposits.
  • Fixed by consistently use wdiv to calculate current pool / borrower debt.

• Issue 2: Fixing issue 1 uncovered bug in updating t0DebtInAuction when auction settled with repayDebt (A1 invariant violation)

  • auction was settled but the quote token amount calculated to repay was rounded down to 0
  • since t0 debt in auction accumulator was updated only when token amount to repay was not 0, the t0debtInAuction accumulator wasn't updated, leaving it in an inconsistent state
  • Fixed by always updating t0debtInAuction accumulator when there's a t0 auction debt change and not constrained by the amount of quote tokens to be paid (same applied in case of pledged collateral too): https://github.com/ajna-finance/contracts/pull/876/commits/05460ba0aea31d1220493b148b6bdc93aacdf930

Contract size

Pre Change

============ Deployment Bytecode Sizes ============
  ERC721Pool               -  24,404B  (99.30%)
  ERC20Pool                -  23,632B  (96.15%)

Post Change

============ Deployment Bytecode Sizes ============
  ERC721Pool               -  24,404B  (99.30%)
  ERC20Pool                -  23,632B  (96.15%)

[grandizzy]

closing in favor of https://github.com/ajna-finance/contracts/pull/886