LockstakeClipper Callee

[valiafetisov]

This PR implements callee contract for the LockstakeClipper using UniswapV2. It allows anyone to participate in auctions using UniswapV2 path to exchange MKR (or NGT) into DAI (or NST).

Notes:

• CI is expected to fail due to the tests for other callees being fragile / depending on the market
  • To test this specific callee, one can run forge test --match-contract=UniswapV2LockstakeCalleeTest locally
• In order to write tests for the new callee, we had to update dependencies and remove hardcoded solidity version at the foundry level (--use solc:0.6.12) while strictly setting it in every callee contract instead. This is due to LockstakeEngine requiring at least 0.8.21 solidity version
  • If requested, those changes could be moved into a separate maintenance PR to keep git history clean
• Current version of the callee support any UniV2 paths that start from MKR or NGT and end with DAI or NST (in other words both MKR/DAI and NGT/NST pools are supported, but not only). The previous version of the callee (found at 9b5cb11) required a redeployment to support different destination token
  • Please let us know which contract design is preferable

[DaiFoundation-DevOps]

All committers have signed the CLA.

[oldchili]

All changes look good, I'm not able to resolve the comments, so please do that on your side.