Handle stdin backpressure in NodeBridge and OptimizedNodeBridge

[bbopen]

Summary

Both NodeBridge and OptimizedNodeBridge write to stdin without handling backpressure (write() return false). Large/rapid requests can fill the pipe buffer and cause memory pressure or dropped writes.

Failure mode

• stdin.write returns false and data queues without flow control.
• Under load, memory grows or writes fail unpredictably.

Repro (adversarial)

• Send a burst of large payloads (e.g., 1000 requests with large args) and observe stdin.write returning false.
• Check for memory growth or rejected writes.

Acceptance criteria

• If stdin.write returns false, wait for drain before sending more data.
• Clear error messaging if the pipe is closed.
• Adversarial stress test confirms no unbounded memory growth or dropped writes.

[bbopen]

Fixed in PR #160: Added writeQueueTimeoutMs option (default: 30000ms) with queuedAt tracking. Queued writes that wait too long are rejected with BridgeTimeoutError.