Use Laravel Pint for code formatting

[datlechin]

Fixes #0000

Changes proposed in this pull request: This PR introduces changes to enhance the code formatting of the PHP files in the repository using Laravel Pint and uses PER coding style.

• Introduction of .github/workflows/pint.yml for automated PHP formatting using Laravel Pint.
• Removal of .styleci.yml as Laravel Pint's PER style now governs formatting.

For reference, an example commit reflecting the code formatting action can be found here: https://github.com/flarum/framework/commit/f06945dd06564865e72943e40680ec448bd793af

These changes optimize code formatting and consistency, aligning with Laravel and PER standards. I would appreciate your review and feedback.

QA

Necessity

• [ ] Has the problem that is being solved here been clearly explained?
• [ ] If applicable, have various options for solving this problem been considered?
• [ ] For core PRs, does this need to be in core, or could it be in an extension?
• [ ] Are we willing to maintain this for years / potentially forever?

Confirmed

• [ ] Frontend changes: tested on a local Flarum installation.
• [ ] Backend changes: tests are green (run composer test).
• [ ] Core developer confirmed locally this works as intended.
• [ ] Tests have been added, or are not appropriate here.

Required changes:

• [ ] Related documentation PR: (Remove if irrelevant)
• [ ] Related core extension PRs: (Remove if irrelevant)