Add Advanced Reasoning section with depth parameter note

[HezziCode]

Summary

Added a new "Advanced Reasoning" section in agents.md explaining the reasoning parameter in ModelSettings.

Details

• Introduced the strategy and depth options for advanced reasoning.
• Noted that the maximum value for the depth parameter is currently undocumented.
• Recommended that contributors start with low values (like 2–3) to avoid excessively long computations or errors.

Motivation

This addition clarifies the usage of the reasoning parameter and helps contributors avoid unintended issues due to missing documentation about depth.

[seratch]

We don't have these parameters in this SDK.