* Add support for O3-mini
- Add support for the o3 mini set of models, including tests that match the constraints in OpenAI's API docs (https://platform.openai.com/docs/models#o3-mini).
* Deprecate and refactor
- Deprecate `ErrO1BetaLimitationsLogprobs` and `ErrO1BetaLimitationsOther`
- Implement `validationRequestForReasoningModels`, which works on both o1 & o3, and has per-model-type restrictions on functionality (eg, o3 class are allowed function calls and system messages, o1 isn't)
* Move reasoning validation to `reasoning_validator.go`
- Add a `NewReasoningValidator` which exposes a `Validate()` method for a given request
- Also adds a test for chat streams
* Final nits
