use pre allocated buffer in Stash.xs

[atoomic]

convert_dotted_string can benefit from
a pre allocated buffer, avoiding the malloc + free.

[toddr]

@atoomic do we have any metrics to show this is faster?

[atoomic]

performance stay very close, we avoid a malloc/free

                          Rate get_set_normal get_set_buffer
get_set_normal 29.675+-0.042/s             --          -2.1%
get_set_buffer 30.302+-0.023/s    2.11+-0.16%             --
                          Rate get_set_normal get_set_buffer
get_set_normal 22.538+-0.044/s             --          -1.9%
get_set_buffer 22.985+-0.038/s    1.99+-0.26%             --

use strict;
use warnings;
use lib qw( ./lib ../lib ../blib/lib ../blib/arch ./blib/lib ./blib/arch );
use Template::Constants qw( :status );
use Template;
use Template::Test;
use Template::Stash::XS;

my $count = 20;
my $data = {
    foo => 10,
    bar => {
        baz => 20,
    },
    something => {
      longer => {
         than => {
          usual => 12345
         }
      }
    },
};

use Benchmark::Dumb qw(:all);

my $stash = Template::Stash::XS->new($data);

print "... check\n";
match( $stash->get('bar.baz'), 20 );
match( $stash->get('something.longer.than.usual'), 12345 );
#match( $stash->get('str_eval_die'), '' );

match( $stash->get2('bar.baz'), 20 );
match( $stash->get2('something.longer.than.usual'), 12345 );

print "... done\n";

compare( "bar.baz" );
compare( 'something.longer.than.usual' );

exit;

sub compare {
  my ( $input ) = @_;

  cmpthese(
      0.01,    # 1% precision
      {   get_set_normal => sub {
              foreach my $i ( 1..1000 ) {
                $stash->get( $input ); 
                $stash->set( $input, $i ); 
                $stash->set( "$i.$i.$i.$i.$i.$i.$i.$i", $i ); 
              }
              
          },
          get_set_buffer => sub {
              foreach my $i ( 1..1000 ) {
                $stash->get2( $input ); 
                $stash->set2( $input, $i );
                $stash->set2( "$i.$i.$i.$i.$i.$i.$i.$i", $i );
              }

          },
      }
  );

}