Test collection fails: starlette 1.3.1 requires httpx2 but tests use httpx

[sei-ahouseholder]

Summary

Starlette 1.3.1 (merged via PR #983) deprecates httpx in favor of httpx2 for use with starlette.testclient. Since filterwarnings = ["error"] is set in pyproject.toml, this deprecation warning is promoted to an error and causes collection to fail for three test packages.

Affected test paths

ERROR test/adapters/driven/test_delivery_inbox_url.py
ERROR test/adapters/driving/fastapi
ERROR test/demo

Error

starlette.exceptions.StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.

Fix

Replace httpx with httpx2 in dev dependencies (and any import httpx in test/adapter code that relies on starlette.testclient), or pin starlette < 1.3.1 until migration is complete.

Reproduction

uv run pytest test/adapters/driven/test_delivery_inbox_url.py

Introduced by the starlette upgrade in PR #983.

[sei-ahouseholder]

Claimed on branch bug/985-httpx2-migration.

[sei-ahouseholder]

Broadening the fix: httpx is no longer maintained, httpx2 is its actively-maintained drop-in replacement. So the PR that closes this issue should fully replace httpx with httpx2 throughout the codebase (import httpx2 as httpx is typically sufficient anywhere that httpx is used.

Reference: https://github.com/pydantic/httpx2