Set GasPrice to 0 for gas estimation tx

[m-Peter]

Closes: #161

Description

The EOA test account used for signing the transaction that encapsulates the user's TransactionArgs, does not have any funds. This means that if GasPrice is greater than 0, we return:

{
  "jsonrpc": "2.0",
  "id": 1,
  "error": {
    "code": -32000,
    "message": "insufficient funds for gas * price + value"
  }
}

By setting this argument to 0, we now return the intrinsic gas, which is 0xcf08 (or 53000 in decimal). The gas is mainly affected by the length of the data / input field value.

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[devbugging]

I believe like discussed this can be problematic in cases where the execution depends on a specific value provided, hence the estimation would be incorrect.

[m-Peter]

Agreed 👍 Most likely I will open an issue in flow-go, since there's no way to achieve this functionality without exposing a relevant method on the EVM contract.