feat: Support string|array output in FunctionToolCallOutput

[gembancud]

• Update FunctionToolCallOutput to accept string|array for output parameter
• This enables returning structured file/image references from function calls
• Aligns with OpenAI's recent API update for file outputs in tool results
• No breaking changes: existing string outputs continue to work

What:

• [x] New Feature

Description:

twitter Openai released support for image and file inputs inside tool call results. This PR aligns with that

[gembancud]

apologies for not including it but the shape should be documented in the openai api reference here