feat: PoC httpx to httpx2 migration

[yamaceay]

Context

Closes SAP/ai-sdk-python-backlog#10.

What this PR does and why it is needed

This PR introduces two bash scripts which do rule-based HTTPX to HTTPX2 migration.

• poc1.sh (which feat: major release on HTTPX2 migration  #157 is auto-generated from): Does a major release by breaking the already existing httpx imports and switching to httpx2 alternatives. The user needs to install httpx2.
• poc2.sh (which fix: minor release on HTTPX2 migration #158 is auto-generated from): Does only a minor release without breaking anything, so the user is informed that the choice of having httpx is deprecated but still supported.

The question whether we support a breaking change or not may depend on some aspects, e.g., some foundational dependencies might need to be fixed to the versions where httpx is essential.

Definition of Done

• Code is tested (Unit, Integration, E2E)
• Error handling created / updated & covered by the tests above
• Documentation updated
  • Only Public APIs are allowed to be used in documentation/tutorials/sample code
• (Optional) Aligned changes with the JS/TS and Java SDK
• (Optional) Release notes updated -->

[yamaceay]

Currently, both PRs are stuck at openai related timeout errors, which needs to be further investigated

Edit 1: Before the fix, the openai mockers registered a bare URL, e.g., <base>/completions, but the real request always arrived with ?api-version=2025-03-01-preview appended, because the proxy client injects that query param on every call. pytest_httpx2 does exact query-param matching (unlike the old respx which just ignored extra params), so the URL never matched and the mock raised a timeout. So, the fix consists of making each openai/cohere mocker build its registered URL conditionally. (1) If a URL is provided it appends ?api-version=2025-03-01-preview to match exactly what the client sends. (2) If it is none (wildcard), it remains None and continues to match anything, so that the previous behavior for all other 960 tests was already preserved. The next question is also if we can get rid of this exact search and just remove the dependency to the hard-coded api version.

Edit 2: Just found out about this: https://github.com/colin-b/pytest_httpx#matching-on-query-parameters

Edit 3: Regex can be used in URL match queries, so I could easily add a regex which (optionally) accepts the extra api-version URL param

[yamaceay]

FYI now both PRs (#157 and #158) seem to pass CI ✅

Edit: Both failed at this time point due to unfinalized migration of google-genai-related code snippets to httpx2. Meanwhile, since there are a large overlap between those two, I believe it is better to maintain just one version (namely major) rather than the minor, so I closed the minor PR for now in favor of the major release.

[mwien]

Nice! Can you add a summary comment (links to PRs etc) to the investigation ticket?

[alpkom]

If this is a POC, could you please change the PR to a draft?