feat: drop support for php < 8.1, drop support for symfony < 5.4 (WIP)

[Chris53897]

#242

Just a quick view and open for disussion what to do next.
Needs rebasing after the other 2 PRs are merged.

Checklist

• Updated CHANGELOG.md to describe BC breaks / deprecations | new feature | bugfix
• [] Documentation pull request created (if not simply a bugfix)

To Do

• to Discuss

[dbu]

thanks a lot!

the failing tests (apart from the stream_for issue) are probably also about missing mocking that is now detected because of strict typing of 3rd party libraries. do you look into those?

[nunoplopes]

ping, could this be revived? It would be great to remove those unneeded dependencies for PHP 8.
@Chris53897 do you have time to rebase this?

[Chris53897]

I resolved the conflicts. But there are errors. Maybe i have time at end of march to have a deeper look.