refactor(wasapi): centralize stream error handling

[roderickvd]

Make process_input/process_output return Result and remove their error_callback parameter.

[Copilot]

Pull request overview

Refactors the WASAPI backend's stream loops so process_input/process_output return Result<(), Error> instead of ControlFlow<()>, centralizing error emission in the callers (run_input/run_output). Behavior is preserved: on error the error callback is invoked and the loop breaks; on the prior "continue" paths (Ok(0) packet size, buffer-empty), the functions simply return Ok(()) and the outer loop iterates.

Changes:

• process_input/process_output no longer take an error_callback parameter and now propagate errors via ?.
• run_input/run_output handle the returned Result by emitting through error_callback and breaking.

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