Add new Uri class for new PSR-7 implementation

[clue]

This changeset adds a new Uri class that builds on top of our new PSR-7 implementation. This brings us one step closer to eventually replace the dated RingCentral implementation (#331) and eventually support PSR-7 v2 (#513). This is a mostly an internal change, but also exposes the new Uri class as part of our public API. Perhaps most notably, this means the Request and ServerRequest classes will now return instances of our Uri class (#519) instead of using the legacy RingCentral classes. It comes with 100% code coverage and does not otherwise affect the public API, so it should be safe to apply.

This builds on top of the recent changes for the Response and ServerRequest classes (#518 and #519), but this similar to #520 doesn't show a noticeable impact on performance during my benchmarks. As a consequence, I consider this mostly a simple feature addition only.

Once merged, I'll file follow-up PRs to remove any leftover references to the old RingCentral implementation accordingly. If you enjoy this change and want to help us continue to ship more improvements, consider supporting this project, for example by becoming a sponsor ❤️

Builds on top of #520, #519, #518, #480, #432, #370, #170 and others

[SimonFrings]

Nice, let's get this in 👍