sloproxy

fix(translator): emit function_call_arguments.done and make function call stream events idempotent master

- Ensure `response.function_call_arguments.done` is emitted with final arguments (including `{}` for empty args). - Track per-call state so duplicate `step.start` / `step.stop` / `arguments_delta` events do not re-emit redundant output. - Populate `response.output_item.done` and completion payloads from a single normalized function-call argument source. Closes: #4742


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2 changed files