Authentication Docs not accurate

`lms.configure_default_client(api_token="your-token-here")` does not work with the latest main release of lmstudio-python (1.5.0), only the Pre-release ([1.6.0b1 - 2025-10-28] ).

And even then, the prelease does not update the global `_default_api_token` in `configure_default_client` of `sync_api.py`. `_default_api_token` should be made global.

Start by comparing the authentication documentation with lmstudio-python 1.5.0 and the 1.6.0b1 pre-release. Inspect configure_default_client in sync_api.py, especially its handling of _default_api_token. Done means the documented call works for the supported release and the token behavior is accurately documented.

Written by the indexing model from the issue text.