Replace httpx dependency with httpx2

[ricgiland]

The httpx library is no longer being maintained and the repo owner has prevented new pull requests so that it is essentially archived. As such, it likely has unaddressed security vulnerabilities and other issues. Fortunately, the people over at Pydantic have decided to fork the project into httpx2 and maintain it themselves. httpx2 uses the same API and can be a drop-in replacement for httpx. Suggest changing the dependency to httpx2