v2.3.1

v2.3.0 is broken — do not use it.

Fixes a regression in v2.3.0 where the httpx2 dependency was pinned to
>=2.2.0, which fails on Python 3.14 builds missing the _zstd C extension.
Pins httpx2 to >=2.0.0, <2.1.0 and switches all httpx imports to
httpx2 for correct namespace resolution.

• httpx2 is now pinned to >=2.0.0, <2.1.0 — versions 2.1.0+ require the
  compression.zstd stdlib module which is not available in all Python 3.14
  builds.
  (#98)
• All import httpx statements replaced with import httpx2 as httpx (or
  from httpx2 import ...) to ensure correct namespace resolution regardless
  of httpx2 version.
• Added test coverage for HttpxClient
  and HttpxResponse.