Read black options in format_dev script (#5827)
## Summary
Comparing repos with black requires that we use the settings as black,
notably line length and magic trailing comma behaviour. Excludes and
preserving quotes (vs. a preference for either quote style) is not yet
implemented because they weren't needed for the test projects.
In the other two commits i fixed the output when the progress bar is
hidden (this way is recommonded in the indicatif docs), added a
`scratch.pyi` file to gitignore because black formats stub files
differently and also updated the ecosystem readme with the projects json
without forks.
## Test Plan
I added a `line-length` vs `line_length` test. Otherwise only my
personal usage atm, a PR to integrate the script into the CI to check
some projects will follow.
