[5/8] Rename Python SDK package to openai-codex (#21905)

## Why

The SDK should publish under the reserved public distribution name
`openai-codex`, and its import module should match that name in the
Python style. Since package names can contain hyphens but import modules
cannot, the public import path becomes `openai_codex`.

Keeping the rename separate from the public API surface change makes the
naming change easy to review and avoids mixing it with API curation.

## What

- Rename the SDK distribution from `openai-codex-app-server-sdk` to
`openai-codex`.
- Rename the import package from `codex_app_server` to `openai_codex`.
- Keep the runtime wheel as the separate `openai-codex-cli-bin`
dependency.
- Update docs, examples, notebooks, artifact scripts, lockfile metadata,
and tests for the new distribution/module names.

## Stack

1. #21891 `[1/8]` Pin Python SDK runtime dependency
2. #21893 `[2/8]` Generate Python SDK types from pinned runtime
3. #21895 `[3/8]` Run Python SDK tests in CI
4. #21896 `[4/8]` Define Python SDK public API surface
5. This PR `[5/8]` Rename Python SDK package to `openai-codex`
6. #21910 `[6/8]` Add high-level Python SDK approval mode
7. #22014 `[7/8]` Add Python SDK app-server integration harness
8. #22021 `[8/8]` Add Python SDK Ruff formatting

## Verification

- Updated package metadata and public API tests to assert the
distribution and import names.

Co-authored-by: Codex <noreply@openai.com>

sdk/python/src/openai_codex/_version.py

@@ -0,0 +1,37 @@
+from __future__ import annotations
+
+import re
+from importlib.metadata import PackageNotFoundError
+from importlib.metadata import version as distribution_version
+from pathlib import Path
+
+DISTRIBUTION_NAME = "openai-codex"
+UNKNOWN_VERSION = "0+unknown"
+
+
+def package_version() -> str:
+    source_version = _source_tree_project_version()
+    if source_version is not None:
+        return source_version
+
+    try:
+        return distribution_version(DISTRIBUTION_NAME)
+    except PackageNotFoundError:
+        return UNKNOWN_VERSION
+
+
+def _source_tree_project_version() -> str | None:
+    pyproject_path = Path(__file__).resolve().parents[2] / "pyproject.toml"
+    if not pyproject_path.exists():
+        return None
+
+    match = re.search(
+        r'(?m)^version = "([^"]+)"$',
+        pyproject_path.read_text(encoding="utf-8"),
+    )
+    if match is None:
+        return None
+    return match.group(1)
+
+
+__version__ = package_version()