🚀 [Feature]: Sustainably prevent data races

[leonklingele]

Feature Description

The data race "fixed" in https://github.com/gofiber/fiber/pull/2368/files wasn't fixed at all.

Instead we should do something à la:

func (s *Storage) ConnLocked(fn func(map[string]entry)) {
    s.mux.Lock()
    defer s.mux.Unlock()
    fn(s.db)
}

Additional Context (optional)

No response

Code Snippet (optional)

No response

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my suggestion prior to opening this one.
• I understand that improperly formatted feature requests may be closed without explanation.

[Hrily]

Hey folks

I've raised a PR #2669 to fix this.

It also adds a unit test to check for race condition, which would otherwise fail in older implementation or without using lock.