fix: time out stalled streams

[victor0602]

What changed

• Apply a timeout while waiting for streaming response headers.
• Add a resettable idle timeout between response body chunks.
• Abort and cancel the underlying reader when a stream stalls or its consumer cancels.
• Allow active streams to continue beyond a single timeout interval.

Why

Streaming requests previously removed the timeout signal entirely and could hang forever when a server stopped sending data.

Impact

Stalled streams now fail predictably and release their resources, while healthy long-running streams continue normally.

Checks

• bun test — 453 passed
• bun run typecheck
• bun run lint — no errors; one pre-existing test warning
• git diff --check

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