Utilize specialized zip iterator impl

Utilize specialized zip iterator impl

 name                        old ns/iter  new ns/iter  diff ns/iter   diff %  speedup
 fmt::write_str_macro1       13,927       12,489             -1,438  -10.33%   x 1.12
 fmt::write_str_macro2       24,633       23,418             -1,215   -4.93%   x 1.05
 fmt::write_str_macro_debug  234,633      233,092            -1,541   -0.66%   x 1.01
 fmt::write_str_ref          5,819        5,823                   4    0.07%   x 1.00
 fmt::write_str_value        6,012        5,828                -184   -3.06%   x 1.03
 fmt::write_vec_macro1       18,550       17,143             -1,407   -7.58%   x 1.08
 fmt::write_vec_macro2       30,369       28,920             -1,449   -4.77%   x 1.05
 fmt::write_vec_macro_debug  244,338      244,901               563    0.23%   x 1.00
 fmt::write_vec_ref          5,952        5,885                 -67   -1.13%   x 1.01
 fmt::write_vec_value        5,944        5,894                 -50   -0.84%   x 1.01