Function fast_cost_from_decoded 

pub fn fast_cost_from_decoded(
    opcode_byte: u8,
    args: &Args,
    pc: u32,
    code: &[u8],
    bitmask: &[u8],
    mem_cycles: u8,
) -> FastCost

Compute FastCost using pre-decoded branch target from Args.

For non-branch instructions, identical to fast_cost_from_raw. For branches, avoids the redundant extract_branch_target_raw call which re-computes skip distances and re-decodes args just to extract the branch offset.