Warn with stacklevel=2 to show caller of deprecation

[hugovk]

Summary

With httpx==0.27.0, I'm getting deprecation warnings like:

/Users/hugo/my-project/.tox/py312/.venv/lib/python3.12/site-packages/httpx/_client.py:680: DeprecationWarning: The'app'shortcutisnowdeprecated. Usetheexplicitstyle'transport=WSGITransport(app=...)'instead.
warnings.warn(message, DeprecationWarning)
--Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

This points to where the deprecated code is in HTTPX and isn't actionable for me.

Instead, if would be more helpful to point to where the deprecated code is being called from, so I can fix my code (or report to the library).

Adding stacklevel=2 gives:

/Users/hugo/my-project/.tox/py312/.venv/lib/python3.12/site-packages/litestar/testing/client/sync_client.py:77: DeprecationWarning: The'app'shortcutisnowdeprecated. Usetheexplicitstyle'transport=WSGITransport(app=...)'instead.
Client.__init__(
--Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

(Aha, so Litestar needs fixing! And they've already fixed and released: litestar-org/litestar#3140, I just need to update 👍)

---

Digging a big deeper, I see there used to be a helper function in httpx/_utils.py:

defwarn_deprecated(message: str) ->None: # pragma: nocover	warnings.warn(message, DeprecationWarning, stacklevel=2)	

It was introduced in #963, and removed in #1597.

Should we add it back?

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• [n/a?] I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• [n/a?] I've updated the documentation accordingly.

[hugovk]

Oops, didn't mean to close this, it was autoclosed when I reset my master back to upstream :)

[lovelydinosaur]

Thanks @hugovk - I think a number of these are removed from the version-1.0 branch.
Should this PR be retargeted?

[hugovk]

Nice, all but three have been removed. I've rebased on version-1.0 and retargeted the version-1.0 branch.

[lovelydinosaur]

Thanks Hugo. ☺️