[POC]: Example of permit2 support on swap router

[ChefMist]

This is a POC

• lot of test cases will fail, so deleted most of them.
• can't just forge install https://github.com/pancakeswap/permit2 as its on a fixed solidity version 0.8.17 and somehow has via_ir=true -- so copied over some code for now.

see BinSwapRouter.t.sol on how to use SwapRouter if permit2 is integrated.

Old flow
Assume swap token X for token Y and a new user.

1. txn 1: approve token X to swap router
2. txn 2: call swap router to swap token X to Y

New flow
Assume swap token X for token Y and a new user.

1. txn 1: approve token X to Permit2.
2. txn 2: sign permit message and call swap router.multiCall (index 0 is permit, index 1 is swap)

Assume swap token X for token Y and user have approved to permit2 in other PCS product prior eg. universal router v3

1. txn 1: sign permit message and call swap router.multiCall (index 0 is permit, index 1 is swap)

[ChefMist]

would be easier to just see from https://github.com/pancakeswap/pancake-v4-periphery/blob/922d32fddb542febb5a60245cfb45fbc853495df/test/pool-bin/BinSwapRouter.t.sol