Use LatestSigner and don't set GasPrice in ContractBackend

[sebastianst]

• eth/channel: Use types.LatestSigner for all sim backend tests
  • Before, types.EIP155Signers were created in many different places. It is recommended by the geth folks to use types.LatestSigner instead. This was streamlined an there's now a common channel/test.SimSigner that can always be used together with the simulated backend.
  • FundAddress and Test_ConfirmTransaction were adapted to use the new types.DynamicFeeTx.
  • The unused test.GasLimit variable was deleted.
  • The test.GasPrice variable was renamed to InitialGasBaseFee and its description updated.
• eth/channel: Don't set GasPrice in ContractBackend.NewTransactor
  • Setting TransactOpts.GasPrice forces the transactions to be sent as a legacy transaction, instead of a type 2 EIP1559, which results in much higher gas costs.
  • Also remove the SuggestedGasPrice method from the SimulatedBackend, as it is not used anymore, because EIP1559 TXs are now sent everywhere.

Opened as a draft to let @ndzik try it out first if we truly now send EIP1559 txs. Original issue in Erdstall is at https://github.com/perun-network/erdstall-ext/issues/121

[ndzik]

I can confirm that this change has the expected result :+1:

I wrote a small application and this tx uses the updated logic from go-perun to make a contract call and it is of type 2 :muscle: