Refactor BalancerV3Executor to have an inner _swapCallback method with the real swapping logic. Then we have two external methods:
- handleCallback: called by the router. Here we need to remove the first 68 bytes (4 selector + 32 dataOffset + 32 dataLength)
- swapCallback: called by the Vault directly if we are swapping against the executor directly (no router involved)
Took 1 minute
