refactor: Introduce standardized API error

This commit refactors the application's error handling mechanism by introducing a new standardized error type, `types.NewAPIError`. It also renames common JSON utility functions for better clarity.

Previously, internal error handling was tightly coupled to the `dto.OpenAIError` format. This change decouples the internal logic from the external API representation.

Key changes:
- A new `types.NewAPIError` struct is introduced to serve as a canonical internal representation for all API errors.
- All relay adapters (OpenAI, Claude, Gemini, etc.) are updated to return `*types.NewAPIError`.
- Controllers now convert the internal `NewAPIError` to the client-facing `OpenAIError` format at the API boundary, ensuring backward compatibility.
- Channel auto-disable/enable logic is updated to use the new standardized error type.
- JSON utility functions are renamed to align with Go's standard library conventions (e.g., `UnmarshalJson` -> `Unmarshal`, `EncodeJson` -> `Marshal`).

controller/channel.go

@@ -388,7 +388,7 @@ func getVertexArrayKeys(keys string) ([]string, error) {
 		return nil, nil
 	}
 	var keyArray []interface{}
-	err := common.UnmarshalJson([]byte(keys), &keyArray)
+	err := common.Unmarshal([]byte(keys), &keyArray)
 	if err != nil {
 		return nil, fmt.Errorf("批量添加 Vertex AI 必须使用标准的JsonArray格式，例如[{key1}, {key2}...]，请检查输入: %w", err)
 	}