[Feature]: Add seed support to Response #257

Describe the feature you want to add

Add an optional seed field to the Response class to store the random seed used during LLM inference. This allows users to track and reproduce model generations when the underlying model and provider support deterministic seeding.

Describe your proposed solution

Introduce an optional seed: Optional[int] parameter with validation and a corresponding property and update method. Include seed in to_dict(), to_json(), and from_json(), and include it in response equality checks. The default value should be None to indicate that no seed was provided or reported by the LLM provider.

Describe alternatives you've considered, if relevant

No response

Additional context

No response