Can I offer a suggestion. Okay, I'm going to offer a suggestion, whether you will have the time or inclination to do anything with it... :)

I think it would greatly simplify and optimise your algorithm to avoid the conditionals associated with negative numbers. You can do that by applying a simple sort to the inputs and then adjusting the whole array to make it all positive (and undo it on output):

sub partition {
    my @numbers - sort{ $b <=> $a } @_;
    my $adjust = 0;
    if( $numbers[ -1 ] < 0 ) {
        $adjust = - $number[ -1 ];
        $_ += $adjust for @numbers;
    }
     
    ...

    $_ -= $adjust for @part_1, @part_2;
    return \@part_1, \@part_2;
}
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Note: I attempted to make this change and offer it back to you, but there is something about your algorithm that I am not understanding, because my attempts disappear up their own jackssies (sp?:).