Deps cleanup PR 3: Drop httpx and requests from vespa/application.py

[thomasht86]

Part of #1285.

Background

We want to minimize pyvespa's runtime dependency surface (see #1285). The httpx → httpr migration is mostly done, but application.py still carries httpx and requests for backwards-compat type hints and exception handling.

Scope

Drop import httpx and import requests from vespa/application.py. This is the most impactful PR in the series — it includes a public API break.

May be split into 3a + 3b during review if it gets heavy:

Part 3a — Remove httpx type-hint shim

• application.py:38 — drop import httpx
• application.py:2050 — timeout: Union[httpx.Timeout, int, float] → Union[int, float]. Drop the isinstance(timeout, httpx.Timeout) branch + DeprecationWarning at lines 2141–2147. The deprecation warning has been live a while — check git blame application.py | grep httpx.Timeout to confirm the window
• application.py:2052 — client: Optional[Union[httpx.AsyncClient, httpr.AsyncClient]] → Optional[httpr.AsyncClient]
• application.py:325-326, 371-373, 387 — same on the sync get_async_session factory
• Update docstrings (lines 348–387, 885, 1038, 1051, 1094, 1106) that say httpx.AsyncClient
• tests/unit/test_application.py:20 — drop import httpx; remove any test constructing httpx.Timeout / httpx.AsyncClient

Part 3b — Remove requests (exceptions + type hints)

• application.py:14-16 — drop from requests import Session, Response, ConnectionError, HTTPError, JSONDecodeError
• _is_connection_error (line 71) — requests.ConnectionError is mostly redundant with the builtin ConnectionError plus httpr.RequestError / httpr.ConnectError that the function already checks
• raise_for_status (line 190) — currently raises requests.HTTPError. Define vespa.exceptions.HTTPError and raise that instead
• JSONDecodeError — switch to json.JSONDecodeError (stdlib)
• Session / Response type hints at lines 14-15 are dead weight on a path that returns httpr.Response. Drop or replace with a Protocol
• Docstrings at lines 426, 1425 mention requests.Session → update to httpr.Client
• Update the comment at line 207 (# Check if response has raise_for_status method (requests/httpx))

Public API impact

Breaking changes for downstream:

1. Passing httpx.Timeout to VespaAsync raises TypeError. Mitigation: the DeprecationWarning has been live for a while; remove cleanly and call out in changelog.
2. Passing httpx.AsyncClient to VespaAsync raises TypeError. Mitigation: require httpr.AsyncClient, call out in changelog.
3. Catching requests.HTTPError from raise_for_status no longer works. Mitigation: export vespa.exceptions.HTTPError AND keep vespa.exceptions.HTTPError = requests.HTTPError style alias for one release if/while requests is still in dev extras — OR just bump the minor version and call it out.

Recommend: re-export HTTPError from vespa.exceptions with a one-release deprecation alias.

Tasks

• Part 3a: drop import httpx and all httpx.* type hints
• Part 3a: update docstrings
• Part 3a: update tests/unit/test_application.py (drop httpx import + adjust tests)
• Part 3b: define vespa.exceptions.HTTPError
• Part 3b: update raise_for_status, _is_connection_error
• Part 3b: drop from requests ... imports
• Part 3b: update unit tests (mocks of requests.Response)
• Add CHANGELOG entry covering the breaking changes
• Verify: grep -rn 'import httpx\|from httpx\|import requests\|from requests' vespa/ returns no hits

Out of scope

• Removing the three deps from pyproject.toml — that's PR 4 (Deps cleanup PR 4: Remove requests/requests_toolbelt/httpx from pyproject.toml #1289)

Risk

Medium. The public API break is real but contained. Most users probably already get an httpr.AsyncClient back from app.get_async_session() and don't construct httpx types themselves, but it's worth a release-notes call-out.