Ability to Use ClaudeSDK Client from multiple async contexts

```
Caveat: As of v0.0.20, you cannot use a ClaudeSDKClient instance across
different async runtime contexts (e.g., different trio nurseries or asyncio
task groups). The client internally maintains a persistent anyio task group
for reading messages that remains active from connect() until disconnect().
This means you must complete all operations with the client within the same
async context where it was connected. Ideally, this limitation should not
exist.
```

Can we please work on fixing [this](https://github.com/anthropics/claude-agent-sdk-python/blob/main/src/claude_agent_sdk/client.py#L55)?

Thanks