perf(stream): channel-based iteration, drop locks

[0x676e67]

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[Copilot]

Pull Request Overview

This PR refactors the stream iterator implementation to use channel-based iteration instead of mutex-protected streams, improving performance by eliminating lock contention.

• Replaces Arc<Mutex<Option<BytesStream>>> with mpsc::Receiver<wreq::Result<Bytes>>
• Spawns a background task to feed stream data into the channel
• Updates error handling to provide more specific messages for channel states

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/error.rs	Updates StopAsyncIteration error to include TryRecvError for better channel error handling
src/client/response/stream.rs	Refactors Streamer to use MPSC channels instead of mutex-protected streams

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