[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/tests/test_public_api_runtime_behavior.py

@@ -7,9 +7,9 @@ from types import SimpleNamespace
 
 import pytest
 
-import codex_app_server.api as public_api_module
-from codex_app_server.client import AppServerClient
-from codex_app_server.generated.v2_all import (
+import openai_codex.api as public_api_module
+from openai_codex.client import AppServerClient
+from openai_codex.generated.v2_all import (
     AgentMessageDeltaNotification,
     ItemCompletedNotification,
     MessagePhase,
@@ -17,8 +17,8 @@ from codex_app_server.generated.v2_all import (
     TurnCompletedNotification,
     TurnStatus,
 )
-from codex_app_server.models import InitializeResponse, Notification
-from codex_app_server.api import (
+from openai_codex.models import InitializeResponse, Notification
+from openai_codex.api import (
     AsyncCodex,
     AsyncThread,
     AsyncTurnHandle,