feat: unify php_server logic

[AlliBalliBaba]

Currently the concept of a php_server only exists on the caddy side and not the FrankenPHP side.
Lately we have been moving more and more in a direction of scoping requests or workers to specific php_server blocks.

This PR is an attempt at refactoring the current php_server logic so it is properly mirrored on the FrankenPHP side without BC breaks for library users (and to prevent future bugs like mentioned in #2487)

[AlliBalliBaba]

Some more small fixes by @nicolas-grekas are now merged in (see #2565)

I also added some tweaks to make startups race-free.

• ServeHTTP() will now block up to 10s waiting until Init() has finished, making it impossible to send requests before startup. (the http server start can happen before the FrankenPHP start)
• Shutdown() will now always wait for Startup() to finish, removing any potential race detections (mainly annoying in tests)

[AlliBalliBaba]

Makes much more sense to not return the same app instance. Probably was the root cause of many subtle bugs in tests

[AlliBalliBaba]

I'll probably merge this branch soon if that's fine with everyone involved . Otherwise we'll just end up stalling other PRs

[dunglas]

I'm trying to tag a release. I hope it will be good tomorrow.

Please wait for the new release to be tagged before merging, so we'll have more time to test this when merged in main.

[AlliBalliBaba]

Looking through global options again, it probably also makes sense to move maxWaitTime and maxRequests to Server. So maybe an extensible api like this would still be preferrable?

server := NewServer(root string, opts... ServerOption )

func WithServerLogger(logger) ServerOption
func WithServerMaxRequests(num) ServerOption
...

[dunglas]

I agree, it feels like we'll add more options in the future

[henderkes]

Let's get this merged first 😆 . There are plenty other features waiting on this too.

[AlliBalliBaba]

Added the server options just to not have BC breaks. Ready to merge whenever

[AlliBalliBaba]

Will merge if there's no other blocker @dunglas. There's still some more cleanup to do, doesn't need to all be in this PR though.

[dunglas]

LGTM!

LGTM