message: fix to PC constraint
diff: @@ -237,10 +237,8 @@ pub fn constraint<F: Field>(memory: Vec<F>) -> (Expr<F>) {
  // * Check next program counter (pc update)
  // need to fix it
  constraints.push(
  - fPC_JNZ * dst *
  - ( (next_pc - (pc + op1)) // <=> pc_up = 4 :
  - + res * (next_pc - (pc+size) ) ) // and dst != 0 : next_pc = pc + op1 // condition holds
  - - (1-dst*res) * (pc+size) ) // <=> pc_up = 4 : if dst == 1 else pc + size )
  + fPC_JNZ * dst * res * (next_pc - (pc + op1)) // <=> pc_up = 4 and dst != 0 : next_pc = pc + op1 // condition holds
  + + fPC_JNZ * (1 - dst) * (next_pc - (pc+size)) // <=> pc_up = 4 and dst == 0 : next_pc = pc + size // condition false
  + (1 - fPC_JNZ) * next_pc // <=> pc_up = {0,1,2} : next_pc = ... // not a conditional jump
  - (1 - fPC_ABS - fPC_RES - fPC_JNZ) * (pc + size) // <=> pc_up = 0 : next_pc = pc + size // common case
  - fPC_ABS * res // <=> pc_up = 1 : next_pc = res // absolute jump
  