[codex] Add independent beta release for the Python SDK (#24828)

## Why

`openai-codex` needs a beta release lifecycle without requiring beta
releases of its pinned runtime package. Previously, SDK staging rewrote
its runtime dependency to the SDK version, which made an SDK-only beta
impossible.

## What changed

- Set the initial SDK beta version to `0.1.0b1` and pin it to published
stable `openai-codex-cli-bin==0.132.0`.
- Decoupled SDK release staging from runtime versioning so it preserves
the reviewed exact runtime pin.
- Added a `python-v*` tag workflow that builds and publishes only
`openai-codex` through PyPI trusted publishing.
- Removed the Beta classifier from runtime package metadata for future
runtime publications.
- Regenerated protocol-derived SDK models from the selected stable
runtime package.

`0.132.0` is the newest stable runtime admitted by the checked-in
dependency date fence and retains the Linux wheel family currently used
by SDK CI.

## Release setup

Before pushing `python-v0.1.0b1`, configure PyPI trusted publishing for
the `openai-codex` project with workflow `python-sdk-release.yml`,
environment `pypi`, and job `publish-python-sdk`.

## Validation

- `uv run --frozen --extra dev ruff check src/openai_codex scripts
examples tests`
- Parsed `.github/workflows/python-sdk-release.yml` with PyYAML.
- Built staged release artifacts locally:
`openai_codex-0.1.0b1-py3-none-any.whl` and
`openai_codex-0.1.0b1.tar.gz`.
- Verified wheel metadata pins `openai-codex-cli-bin==0.132.0`.
- Tests are deferred to online CI for this PR.

sdk/python/tests/test_contract_generation.py

@@ -40,7 +40,7 @@ def test_generated_files_are_up_to_date():
 
     # Regenerate contract artifacts via the pinned runtime package, not a local
     # app-server binary from the checkout or CI environment.
-    assert importlib.metadata.version("openai-codex-cli-bin") == "0.131.0a4"
+    assert importlib.metadata.version("openai-codex-cli-bin") == "0.132.0"
     env = os.environ.copy()
     env.pop("CODEX_EXEC_PATH", None)
     python_bin = str(Path(sys.executable).parent)