Add Runtime Validation for name Attribute in Agent Class

[EngineerAbdullahIqbal]

This pull request proposes adding runtime validation to the Agent class in the openai-agents-sdk to ensure the name attribute is a non-empty string. This change addresses the issue where non-string types (e.g., integers or dictionaries) are currently accepted, despite the str type annotation, which can lead to unexpected behavior. By implementing validation, we make the SDK more robust and user-friendly.

Proposed Change

The proposed solution adds a __post_init__ method to the Agent class to validate that name is a string and not empty or whitespace-only. This approach is standard for Python dataclasses and does not affect other attributes or methods.

Why It Matters

This change prevents potential errors, aligns with type annotations, and improves the user experience by providing clear feedback on invalid inputs. It benefits the community by making the SDK more reliable, encouraging adoption, and reducing support overhead.

The __post_init__ method is the most suitable, as it is lightweight, aligns with Python dataclass conventions, and requires minimal changes to the existing codebase.

[seratch]

Thanks for sending this PR! but we're already working on this at #998; please feel free to add comments if you have any.