[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/examples/_bootstrap.py

@@ -47,11 +47,11 @@ def ensure_local_sdk_src() -> Path:
 
 
 def runtime_config():
-    """Return an example-friendly AppServerConfig for repo-source SDK usage."""
-    from openai_codex import AppServerConfig
+    """Return an example-friendly CodexConfig for repo-source SDK usage."""
+    from openai_codex import CodexConfig
 
     ensure_runtime_package_installed(sys.executable, _SDK_PYTHON_DIR)
-    return AppServerConfig()
+    return CodexConfig()
 
 
 def _png_chunk(chunk_type: bytes, data: bytes) -> bytes: