Move router integration tests to router packages

[boesing]

RFC

Q	A
Proposed Version(s)	3.7.0
BC Break?	No

Goal

To unblock PHP 8.1 support from this package, we should remove all router integration tests and only do unit tests when it comes to integration tests (and/or use our own laminas-router where we actually can always provide patches to be compatible with new versions - e.g. PHP or major versions of this package).

Background

mezzio/mezzio-aurarouter does not support PHP 8.1 yet. To provide proper 8.1 support (without deprecation warnings), we would have to provide patches to https://github.com/auraphp/Aura.Router
To avoid having that huge amount of work until we can get this package ready for 8.1, we should move all integration tests to the related components.

Considerations

Users wont have any impact on this as we only require these packages for integration tests.

Proposal(s)

1. Remove all integration tests from here (or keep those we actually can maintain by ourselves)
2. Provide support for PHP 8.1

Appendix

If we do want to keep that package, we should at least remove integration tests from this package and port them to the router component.