[ssccinng]

Motivation & Context

FunctionTool.parse_result handled lists of rich Content and Pydantic models, but tuples bypassed those paths. This could stringify Content objects and serialize models as strings instead of dictionaries.

Description & Review Guide

• Handle tuples like lists during recursive JSON conversion and rich Content preservation.
• Preserve tuple Content items in order, and serialize nested Pydantic models as dictionaries.
• Add regression coverage for tuple and list equivalence, nested tuples, mixed Content and ordinary values, and empty tuples.

Related Issue

N/A - trivial change: fixes tuple handling in function result serialization.

AI Assistance

AI assistance was used for the implementation, regression tests, and this description.

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR links to an agreed issue or documents a trivial-change exception
• This is not a breaking change.