Function fast_cost_lut 

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

Compute FastCost via lookup table — replaces the 256-arm match dispatch with a single array access + lightweight mask computation.