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

reasoning_validator.go

@@ -0,0 +1,111 @@
+package openai
+
+import (
+	"errors"
+	"strings"
+)
+
+var (
+	// Deprecated: use ErrReasoningModelMaxTokensDeprecated instead.
+	ErrO1MaxTokensDeprecated                   = errors.New("this model is not supported MaxTokens, please use MaxCompletionTokens")                               //nolint:lll
+	ErrCompletionUnsupportedModel              = errors.New("this model is not supported with this method, please use CreateChatCompletion client method instead") //nolint:lll
+	ErrCompletionStreamNotSupported            = errors.New("streaming is not supported with this method, please use CreateCompletionStream")                      //nolint:lll
+	ErrCompletionRequestPromptTypeNotSupported = errors.New("the type of CompletionRequest.Prompt only supports string and []string")                              //nolint:lll
+)
+
+var (
+	ErrO1BetaLimitationsMessageTypes = errors.New("this model has beta-limitations, user and assistant messages only, system messages are not supported")       //nolint:lll
+	ErrO1BetaLimitationsTools        = errors.New("this model has beta-limitations, tools, function calling, and response format parameters are not supported") //nolint:lll
+	// Deprecated: use ErrReasoningModelLimitations* instead.
+	ErrO1BetaLimitationsLogprobs = errors.New("this model has beta-limitations, logprobs not supported")                                                                               //nolint:lll
+	ErrO1BetaLimitationsOther    = errors.New("this model has beta-limitations, temperature, top_p and n are fixed at 1, while presence_penalty and frequency_penalty are fixed at 0") //nolint:lll
+)
+
+var (
+	//nolint:lll
+	ErrReasoningModelMaxTokensDeprecated = errors.New("this model is not supported MaxTokens, please use MaxCompletionTokens")
+	ErrReasoningModelLimitationsLogprobs = errors.New("this model has beta-limitations, logprobs not supported")                                                                               //nolint:lll
+	ErrReasoningModelLimitationsOther    = errors.New("this model has beta-limitations, temperature, top_p and n are fixed at 1, while presence_penalty and frequency_penalty are fixed at 0") //nolint:lll
+)
+
+var unsupportedToolsForO1Models = map[ToolType]struct{}{
+	ToolTypeFunction: {},
+}
+
+var availableMessageRoleForO1Models = map[string]struct{}{
+	ChatMessageRoleUser:      {},
+	ChatMessageRoleAssistant: {},
+}
+
+// ReasoningValidator handles validation for o-series model requests.
+type ReasoningValidator struct{}
+
+// NewReasoningValidator creates a new validator for o-series models.
+func NewReasoningValidator() *ReasoningValidator {
+	return &ReasoningValidator{}
+}
+
+// Validate performs all validation checks for o-series models.
+func (v *ReasoningValidator) Validate(request ChatCompletionRequest) error {
+	o1Series := strings.HasPrefix(request.Model, "o1")
+	o3Series := strings.HasPrefix(request.Model, "o3")
+
+	if !o1Series && !o3Series {
+		return nil
+	}
+
+	if err := v.validateReasoningModelParams(request); err != nil {
+		return err
+	}
+
+	if o1Series {
+		if err := v.validateO1Specific(request); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// validateReasoningModelParams checks reasoning model parameters.
+func (v *ReasoningValidator) validateReasoningModelParams(request ChatCompletionRequest) error {
+	if request.MaxTokens > 0 {
+		return ErrReasoningModelMaxTokensDeprecated
+	}
+	if request.LogProbs {
+		return ErrReasoningModelLimitationsLogprobs
+	}
+	if request.Temperature > 0 && request.Temperature != 1 {
+		return ErrReasoningModelLimitationsOther
+	}
+	if request.TopP > 0 && request.TopP != 1 {
+		return ErrReasoningModelLimitationsOther
+	}
+	if request.N > 0 && request.N != 1 {
+		return ErrReasoningModelLimitationsOther
+	}
+	if request.PresencePenalty > 0 {
+		return ErrReasoningModelLimitationsOther
+	}
+	if request.FrequencyPenalty > 0 {
+		return ErrReasoningModelLimitationsOther
+	}
+
+	return nil
+}
+
+// validateO1Specific checks O1-specific limitations.
+func (v *ReasoningValidator) validateO1Specific(request ChatCompletionRequest) error {
+	for _, m := range request.Messages {
+		if _, found := availableMessageRoleForO1Models[m.Role]; !found {
+			return ErrO1BetaLimitationsMessageTypes
+		}
+	}
+
+	for _, t := range request.Tools {
+		if _, found := unsupportedToolsForO1Models[t.Type]; found {
+			return ErrO1BetaLimitationsTools
+		}
+	}
+	return nil
+}