chore: refactor code using arrow functions

[datlechin]

Utilize arrow functions for shorter and more readable code

Fixes #0000

Changes proposed in this pull request:

Reviewers should focus on:

Screenshot

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)

[SychO9]

Thanks for the PR!

In some places it is less readable to use arrow functions, I think it would be better to keep things as is and only change when it makes sense or use for newer code when it makes sense. what do you think?

[datlechin]

I see, will reopen a new PR for this.