fix: saturation check

[sstadick]

Previously this was subtracting the negative score from the v_pos_limit, which is more negative than needed.

def main():
    var neg_score: UInt8 = 10
    var max_score: UInt8 = 5
    var checkpoint = min(UInt8.MAX - neg_score, UInt8.MAX - max_score)

    var new_score = 1 - neg_score
    print("Score underflow", new_score)
    if new_score >= checkpoint:
        print("saturation risk")

    new_score = 250 + max_score
    if new_score >= checkpoint:
        print("saturation risk")
    print("Score max", new_score)