A little less obfuscated if you use extended regex comments. (I liked this solution a lot, because I feel like it gets to the "core" of what is wanted.)

use strict;
use warnings;
use Data::Dumper;

print join " ", splitter('xx((556xx');

sub splitter {
  local $_ = shift;
  split /
           (?<!^)                                    #not preceeded by
+ start of string.
           (?!                                     #not followed by...
               (??{ 
                   quotemeta substr($_, $-[0]-1, 1)     # the escaped 
+(quote-metad) last character of the last match.
                                                   # note: $-[0] is th
+e offset of start of last successful match.
                                                   # $-[1] (not used h
+ere) would be the offset of start of the first sub pattern.
                  })
           )
           /x;      
}
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