chore: align multi_agents write_to_file with backend UTF-8 handling

[PriscaAmajuoyi]

Summary

This PR makes the multi-agents file export utility more robust by aligning its write_to_file implementation with the existing backend write_to_file helper. It ensures that any non-string text is coerced to a string before UTF-8 encoding.

Changes

• File: multi_agents/agents/utils/file_formats.py

  • Updated write_to_file:

    async def write_to_file(filename: str, text: str) -> None:
        """Asynchronously write text to a file in UTF-8 encoding.
    
        Args:
            filename (str): The filename to write to.
            text (str): The text to write.
        """
        # Ensure text is a string
        if not isinstance(text, str):
            text = str(text)
    
        # Convert text to UTF-8, replacing any problematic characters
        text_utf8 = text.encode('utf-8', errors='replace').decode('utf-8')
    
        async with aiofiles.open(filename, "w", encoding='utf-8') as file:
            await file.write(text_utf8)

• This mirrors the behavior already used in backend/utils.py, so both single-agent and multi-agents flows handle non-string text consistently.

Rationale

• In some paths, text may not be a plain str (e.g., other types or objects with a __str__ representation).
• Backend write_to_file already handles this case; this change brings the multi-agents version in line, reducing the chance of unexpected encoding errors.

Testing

• Verified by inspection that:
  • Non-string text will now be converted via str(text) before encoding.
  • UTF-8 encoding with errors='replace' is preserved.
• No changes were made to the public API or other functions; this is a small internal robustness improvement.