[1.x] Makes Pint 40x faster

[nunomaduro]

this pull request adds the --parallel option to laravel pint, enabling it to fully leverage the parallel capabilities of php cs fixer. the results are just insane:

the “40x” faster claim, is on the first run, and will depend on your laptop, but on mine: Apple M4 Max 36GB Ram.

laravel project with 1936 files:  
before: 2 minutes 🐌🐌  
after:  3 seconds 🏎️💨

laravel project with 989 files:
before: 41 seconds 🐌🐌  
after:  1 second 🏎️💨

this feature has actually been in php cs fixer for a while — we just hadn’t been using it until now. 🤷🏻‍♂️

finally, this new feature should be considered experimental and potentially unstable. therefore, i’ve added the experimental wording to the optional flag --parallel, so people can try it out in the meantime.