[codex] Rename Python SDK AppServerConfig to CodexConfig (#24800)

## Why

`AppServerConfig` is exported as part of the ergonomic Python SDK
surface and passed to `Codex(...)` and `AsyncCodex(...)`. That name
exposes the underlying app-server transport at the same layer where
users are configuring the Codex client. `CodexConfig` makes the common
callsite read naturally and names the object it configures.

## What changed

- Renamed the public configuration dataclass from `AppServerConfig` to
`CodexConfig`.
- Updated `Codex`, `AsyncCodex`, and the transport clients to accept
`CodexConfig`.
- Updated binary-resolution messages, package exports, docs, examples,
and related coverage to use the new public name.

## API impact

```python
from openai_codex import Codex, CodexConfig

with Codex(config=CodexConfig(codex_bin="/path/to/codex")) as codex:
    ...
```

Callers should now import and construct `CodexConfig`; `AppServerConfig`
is no longer part of the Python SDK surface.

## Validation

- `uv run --frozen --extra dev ruff check src/openai_codex scripts
examples tests`
- Tests are deferred to online CI for this PR.

sdk/python/tests/test_async_client_behavior.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 import asyncio
 import time
 
-from openai_codex.async_client import AsyncAppServerClient
+from openai_codex.async_client import AsyncCodexClient
 from openai_codex.generated.v2_all import (
     TurnCompletedNotification,
 )
@@ -15,7 +15,7 @@ def test_async_client_allows_concurrent_transport_calls() -> None:
 
     async def scenario() -> int:
         """Run two blocking sync calls and report peak overlap."""
-        client = AsyncAppServerClient()
+        client = AsyncCodexClient()
         active = 0
         max_active = 0
 
@@ -40,7 +40,7 @@ def test_async_client_turn_notification_methods_delegate_to_sync_client() -> Non
 
     async def scenario() -> tuple[list[tuple[str, str]], Notification, str]:
         """Record the sync-client calls made by async turn notification wrappers."""
-        client = AsyncAppServerClient()
+        client = AsyncCodexClient()
         event = Notification(
             method="unknown/direct",
             payload=UnknownNotification(params={"turnId": "turn-1"}),