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`).

common/str.go

@@ -33,7 +33,7 @@ func MapToJsonStr(m map[string]interface{}) string {
 
 func StrToMap(str string) (map[string]interface{}, error) {
 	m := make(map[string]interface{})
-	err := UnmarshalJson([]byte(str), &m)
+	err := Unmarshal([]byte(str), &m)
 	if err != nil {
 		return nil, err
 	}