Summary

Update httpx2’s cli extra to allow rich 15; update uv.lock so we test with rich 15.

The only documented breaking change in rich 15 is that support for the end-of-life Python version 3.8 was dropped.

https://github.com/Textualize/rich/blob/v15.0.0/CHANGELOG.md

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change. This is covered by existing tests.
• I've updated the documentation accordingly. No documentation changes are required.