fix: use asyncio.to_thread for non-blocking input in async chat examples

[bodapatisaikrishna]

Checklist

• I have read both the CONTRIBUTING.md and Contributor License Agreement documents.
• I have created an issue or feature request and received approval from xAI maintainers. (minor changes like fixing typos can skip this step)
• I have tested my changes locally and they pass all CI checks.
• I have added necessary documentation or updated existing documentation.

Description

In README.md (under Multi-Turn Chat (Asynchronous)) and examples/aio/chat.py, synchronous standard input("You: ") was invoked directly inside coroutines running on the asyncio event loop.

Calling synchronous blocking I/O on the main thread event loop blocks all concurrent background tasks, timeouts, polling timers, and streaming handlers until the user presses Enter.

This change:

1. Updates the async chat snippet in README.md to use prompt = await asyncio.to_thread(input, "You: ").
2. Adds an async helper ainput(prompt) wrapping asyncio.to_thread(input, prompt) in examples/aio/chat.py and updates all chat loops (basic_chat, chat_with_streaming, batch_chat, batch_chat_with_streaming).

Related Issue

Resolves #213

Type of Change

• Bug fix
• Documentation update

Additional Notes

Validated locally:

• uv run ruff format --check: All 124 files formatted.
• uv run ruff check: All checks passed.
• uv run pyright: 0 errors, 0 warnings.
• uv run pytest -q: 831 passed.