Add support for O3-mini (#930)

* 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

chat_stream.go

@@ -80,7 +80,8 @@ func (c *Client) CreateChatCompletionStream(
 	}
 
 	request.Stream = true
-	if err = validateRequestForO1Models(request); err != nil {
+	reasoningValidator := NewReasoningValidator()
+	if err = reasoningValidator.Validate(request); err != nil {
 		return
 	}