Reset trader approval

[nlordell]

Fixes an issue with trade simulations and the Tether USD token for accounts with some approval to the CoW Protocol vault relayer.

Specifically, Tether requires an approval reset before setting a new one, so make sure to do that in the Trader.sol impersonator.

Test Plan

Run the orderbook without this change and perform the following quote:

% curl -s http://localhost:8080/api/v1/quote -X POST -H 'content-type: application/json' --data '@-' <<JSON | jq
{
  "from": "0xf17afe5237d982868b8a97424dd79a4a50c36412",
  "sellToken": "0xdac17f958d2ee523a2206206994597c13d831ec7",
  "buyToken": "0x6b175474e89094c44da98b954eedeac495271d0f",
  "kind": "sell",
  "sellAmountBeforeFee": "1000000000"
}
JSON

Note that before this change, we get an error because of a failed simulation:

{
  "errorType": "InternalServerError",
  "description": ""
}

After, we have great success!

{
  "quote": {
    "sellToken": "0xdac17f958d2ee523a2206206994597c13d831ec7",
    "buyToken": "0x6b175474e89094c44da98b954eedeac495271d0f",
    "receiver": null,
    "sellAmount": "993229180",
    "buyAmount": "993230905247068340318",
    "validTo": 1667581593,
    "appData": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "feeAmount": "6770820",
    "kind": "sell",
    "partiallyFillable": false,
    "sellTokenBalance": "erc20",
    "buyTokenBalance": "erc20",
    "signingScheme": "eip712"
  },
  "from": "0xf17afe5237d982868b8a97424dd79a4a50c36412",
  "expiration": "2022-11-04T16:37:33.530731Z",
  "id": 3
}