Fix temperature not being set to 0 due to json omitempty

The issue was caused by the `omitempty` tag in the Go struct, which prevented the `temperature` field from being included in the JSON output when it was set to 0.

Signed-off-by: Butui Hu <hot123tea123@gmail.com>

dto/openai_request.go

@@ -23,7 +23,7 @@ type GeneralOpenAIRequest struct {
 	MaxTokens           uint            `json:"max_tokens,omitempty"`
 	MaxCompletionTokens uint            `json:"max_completion_tokens,omitempty"`
 	ReasoningEffort     string          `json:"reasoning_effort,omitempty"`
-	Temperature         float64         `json:"temperature,omitempty"`
+	Temperature         *float64        `json:"temperature,omitempty"`
 	TopP                float64         `json:"top_p,omitempty"`
 	TopK                int             `json:"top_k,omitempty"`
 	Stop                any             `json:"stop,omitempty"`