Global timeout

[andybbruno]

Summary

This pull request introduces a new, more straightforward way to configure a global default timeout for all clients and requests in httpx without needing to access the internal _config object. The enhancement is achieved by exposing the DEFAULT_TIMEOUT_CONFIG in the main __init__.py file (see discussion here).

This change simplifies the process, allowing developers to set a global timeout directly and elegantly, like so:

import httpx
httpx.DEFAULT_TIMEOUT_CONFIG = httpx.Timeout(10.0)

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.
• I've updated the documentation accordingly.

[tomchristie]

Thanks @andybbruno - do appreciate your time & interest on this.

The proposal (exposing a global constant as public API) doesn't really match the coding style in other parts of the project,
and I don't think we reached a resolution on #3356. We'd need a clearer consensus before accepting PRs in this direction.