estimateGasFee based on current block

[sakulstra]

Hey, in multiple projects now i wanted to calculate the next baseFeePerGas, without having to do an rpc call, given i already have the current block.

To do it is not so complicated at least for mainnet:

// based on geth https://github.com/ethereum/go-ethereum/blob/509a64ffb9405942396276ae111d06f9bded9221/consensus/misc/eip1559/eip1559.go#L55
function getNextBaseFee(block: Block) {
  const param = 4n; // 4 on eth, 8 on polygon, ...

  const tmp =
    ((block.gasUsed - block.gasLimit / 2n) * block.baseFeePerGas!) /
    block.gasLimit /
    param;
  if (tmp === 0n) return block.baseFeePerGas;
  if (tmp > 0n) return block.baseFeePerGas! + (1n > tmp ? 1n : tmp);
  return 0n > block.baseFeePerGas! + tmp ? 0n : block.baseFeePerGas! + tmp;
}

I think would be good to have this (perhaps in a cleaner form) on utils or similar.