Ruby

str_buf_cat: preserve coderange when going through fastpath

rb_str_modify clear the coderange, which in this case isn't
necessary.

compare-ruby: ruby 3.2.0dev (2022-07-12T15:01:11Z master 71aec68566) [arm64-darwin21]
built-ruby: ruby 3.2.0dev (2022-07-19T07:17:01Z faster-buffer-conc.. 3cad62aab4) [arm64-darwin21]
warming up...

|                      |compare-ruby|built-ruby|
|:---------------------|-----------:|---------:|
|binary_concat_utf8    |    360.617k|  605.091k|
|                      |           -|     1.68x|
|binary_concat_binary  |    446.650k|  605.053k|
|                      |           -|     1.35x|
|utf8_concat_utf8      |    454.166k|  597.311k|
|                      |           -|     1.32x|

|            |compare-ruby|built-ruby|
|:-----------|-----------:|---------:|
|erb_render  |      1.790M|    2.045M|
|            |           -|     1.14x|