get L1Fee From Gas Price Oracle
Get L1 data fee from OP Stack GasPriceOracle predeploy (getL1Fee(bytes)). Uses the RLP-encoded unsigned transaction bytes as input; the oracle computes the L1 portion of the fee based on calldata size. Returns null on any failure.
Return
L1 fee in wei, or null if call fails or chain is not OP Stack
Parameters
unsigned Tx Bytes
RLP-encoded unsigned tx (legacy or type-2) as used for signing