Function calculate_block_gas_limit

pub fn calculate_block_gas_limit(
    parent_gas_limit: u64,
    desired_gas_limit: u64,
) -> u64

Calculate the gas limit for the next block based on parent and desired gas limits. Ref: https://github.com/ethereum/go-ethereum/blob/88cbfab332c96edfbe99d161d9df6a40721bd786/core/block_validator.go#L166