Completely Untested, and theoretical:

use Path::Tiny;
my %name2blob;

sub extract_zip{
  my ($filename) = @_;
  my $nef = path($filename)->basename('.7z');
  my $sts = $nef . ".sts"; 
  my $sevenzcmd="ze e  $filename -y -so ";

  open my $data, "-|", $sevenzcmd . $nef 
         or die "Cannot open 7z $nef:$!";
  $name2blob{$filename}{NEF} = path ($data)->slurp;
  close $data;
  open  $data, "-|", $sevenzcmd . $sts 
         or die "Cannot open 7z $sts:$!";
  $name2blob{$filename}{STS} = path ($data)->slurp;
  close $data;
}
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Hmm - you may need to write your own "slurp" if Path::Tiny->slurp() does not like file handles.

  do { local $/;  <$data> }
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