sdk: launch packaged Codex runtimes (#23786)

## Why

The Python and TypeScript SDKs launch the native Codex runtime directly,
so they need to consume the same package artifact shape that release
jobs now produce. The runtime wheel should be built from the canonical
Codex package archive rather than reconstructing a parallel layout from
loose binaries.

## What Changed

- Stage `openai-codex-cli-bin` by extracting
`codex-package-<target>.tar.gz` into `src/codex_cli_bin` and validating
the expected package layout.
- Update release workflows to pass the generated package archive into
`stage-runtime` instead of the temporary package directory.
- Update Python runtime setup to download `codex-package-*.tar.gz`
release assets directly.
- Expose Python runtime helpers for the bundled package directory and
`codex-path`, and prepend that path when `openai_codex` launches the
installed runtime without duplicating Windows `Path`/`PATH` keys.
- Teach the TypeScript SDK to resolve package-layout optional
dependencies while keeping the existing npm fallback layout, and
preserve the existing Windows path variable casing when prepending
`codex-path`.

## Test Plan

- `python3 -m py_compile sdk/python/scripts/update_sdk_artifacts.py
sdk/python/_runtime_setup.py sdk/python/src/openai_codex/client.py
sdk/python-runtime/src/codex_cli_bin/__init__.py`
- `uv run --frozen --project sdk/python --extra dev ruff check
sdk/python/scripts/update_sdk_artifacts.py sdk/python/_runtime_setup.py
sdk/python/src/openai_codex/client.py
sdk/python/tests/test_artifact_workflow_and_binaries.py
sdk/python-runtime/src/codex_cli_bin/__init__.py`
- `uv run --frozen --project sdk/python --extra dev pytest
sdk/python/tests/test_artifact_workflow_and_binaries.py`
- `pnpm eslint src/exec.ts tests/exec.test.ts`
- `pnpm test --runInBand tests/exec.test.ts`

sdk/python-runtime/src/codex_cli_bin/__init__.py

@@ -1,14 +1,23 @@
-from __future__ import annotations
-
 import os
 from pathlib import Path
 
 PACKAGE_NAME = "openai-codex-cli-bin"
+PACKAGE_METADATA_FILENAME = "codex-package.json"
+
+
+def bundled_package_dir() -> Path:
+    path = Path(__file__).resolve().parent
+    metadata_path = path / PACKAGE_METADATA_FILENAME
+    if not metadata_path.is_file():
+        raise FileNotFoundError(
+            f"{PACKAGE_NAME} is installed but missing its package metadata at {metadata_path}"
+        )
+    return path
 
 
 def bundled_codex_path() -> Path:
     exe = "codex.exe" if os.name == "nt" else "codex"
-    path = Path(__file__).resolve().parent / "bin" / exe
+    path = bundled_package_dir() / "bin" / exe
     if not path.is_file():
         raise FileNotFoundError(
             f"{PACKAGE_NAME} is installed but missing its packaged codex binary at {path}"
@@ -16,4 +25,14 @@ def bundled_codex_path() -> Path:
     return path
 
 
-__all__ = ["PACKAGE_NAME", "bundled_codex_path"]
+def bundled_path_dir() -> Path | None:
+    path = bundled_package_dir() / "codex-path"
+    return path if path.is_dir() else None
+
+
+__all__ = [
+    "PACKAGE_NAME",
+    "bundled_codex_path",
+    "bundled_package_dir",
+    "bundled_path_dir",
+]