[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/notebooks/sdk_walkthrough.ipynb

@@ -6,7 +6,7 @@
    "source": [
     "# Codex Python SDK Walkthrough\n",
     "\n",
-    "Public SDK surface only (`codex_app_server` root exports)."
+    "Public SDK surface only (`openai_codex` root exports)."
    ]
   },
   {
@@ -32,7 +32,7 @@
     "\n",
     "\n",
     "def _is_sdk_python_dir(path: Path) -> bool:\n",
-    "    return (path / 'pyproject.toml').exists() and (path / 'src' / 'codex_app_server').exists()\n",
+    "    return (path / 'pyproject.toml').exists() and (path / 'src' / 'openai_codex').exists()\n",
     "\n",
     "\n",
     "def _iter_home_fallback_candidates(home: Path):\n",
@@ -114,7 +114,7 @@
     "\n",
     "# Force fresh imports after SDK upgrades in the same notebook kernel.\n",
     "for module_name in list(sys.modules):\n",
-    "    if module_name == 'codex_app_server' or module_name.startswith('codex_app_server.'):\n",
+    "    if module_name == 'openai_codex' or module_name.startswith('openai_codex.'):\n",
     "        sys.modules.pop(module_name, None)\n",
     "\n",
     "print('Kernel:', sys.executable)\n",
@@ -130,7 +130,7 @@
    "source": [
     "# Cell 2: imports (public only)\n",
     "from _bootstrap import assistant_text_from_turn, find_turn_by_id, server_label\n",
-    "from codex_app_server import (\n",
+    "from openai_codex import (\n",
     "    AsyncCodex,\n",
     "    Codex,\n",
     "    ImageInput,\n",
@@ -245,7 +245,7 @@
    "source": [
     "# Cell 5b: one turn with most optional turn params\n",
     "from pathlib import Path\n",
-    "from codex_app_server import (\n",
+    "from openai_codex import (\n",
     "    AskForApproval,\n",
     "    Personality,\n",
     "    ReasoningEffort,\n",
@@ -295,7 +295,7 @@
    "source": [
     "# Cell 5c: choose highest model + highest supported reasoning, then run turns\n",
     "from pathlib import Path\n",
-    "from codex_app_server import (\n",
+    "from openai_codex import (\n",
     "    AskForApproval,\n",
     "    Personality,\n",
     "    ReasoningEffort,\n",