Replace httpx with httpx2

### Feature request

Replace the httpx library with the [httpx2](https://github.com/pydantic/httpx2) fork, maintained by Pydantic.

### Motivation

Httpx has not been released since December 2024, and has closed all public access to Issues / Discussions / PRs, this raises questions about the actual state of maintenance and could lead to security issues down the line.

https://github.com/encode/httpx/discussions/3784

### Your contribution

/

No files or tests are named. Start by locating the dependency declaration and every httpx import or use in the repository; done means the project uses httpx2 in place of httpx and the existing test suite passes.

Written by the indexing model from the issue text.