Add Asyncio Support to AISuite

[janvis11]

Summary

This PR introduces asyncio support to aisuite, enabling developers to use the library in modern asynchronous Python applications (FastAPI, async agents, event-driven LLM workflows, chat servers, etc.).

This feature was frequently requested across community discussions and greatly improves the usability of AISuite in production-grade AI systems.

---

Motivation

AISuite currently exposes synchronous methods only.
However, most real-world AI apps — including chat APIs, RAG servers, and multi-tool agents — run on async frameworks where blocking calls limit concurrency and performance.

Adding async support:

• Enables parallel LLM calls without blocking the event loop
• Makes AISuite compatible with FastAPI, async workers, and async agents
• Improves throughput for multi-provider or multi-step pipelines
• Aligns AISuite with modern LLM SDKs which already expose async methods

This PR adds async support without breaking any existing synchronous APIs.

---

What This PR Adds

✔️ AsyncClient wrapper class

• Provides async equivalents of existing sync methods
• Uses asyncio.to_thread() to maintain compatibility with all current provider implementations

✔️ async generate() and async chat() methods

Example:

from aisuite import AsyncClient

client = AsyncClient("openai:gpt-4o")

async def main():
    response = await client.generate("Write a haiku about async LLMs.")
    print(response.text)

✔️ Backward-compatible design

• No changes required for existing users
• Sync and async clients can coexist
• Providers do not need to be modified

✔️ Basic async tests

• Confirms event-loop behavior
• Ensures output matches synchronous results

---

Implementation Details

• Introduced AsyncClient class in aisuite/async_client.py
• Forwarded all calls to async wrappers around existing provider implementations
• Added minimal async examples in docs
• Added lightweight async unit tests under tests/async/

This design keeps AISuite simple while giving developers full async capabilities.

---

Checklist

• Async client implemented
• Tests added
• Documentation updated
• Backward compatible
• Linted and formatted

Thank you!