code formatting

[norci]

There's a github action for julia formatter:
https://github.com/julia-actions/julia-format/blob/master/README.md

and we can use a configuration file to specify the preferred format:
https://domluna.github.io/JuliaFormatter.jl/stable/config/

what about:

1. create a configuration file for JuliaFormatter, in the project root.
2. use julia-actions/julia-format instead of format_pr.yml