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`).

dto/error.go

@@ -1,5 +1,7 @@
 package dto
 
+import "one-api/types"
+
 type OpenAIError struct {
 	Message string `json:"message"`
 	Type    string `json:"type"`
@@ -14,11 +16,11 @@ type OpenAIErrorWithStatusCode struct {
 }
 
 type GeneralErrorResponse struct {
-	Error    OpenAIError `json:"error"`
-	Message  string      `json:"message"`
-	Msg      string      `json:"msg"`
-	Err      string      `json:"err"`
-	ErrorMsg string      `json:"error_msg"`
+	Error    types.OpenAIError `json:"error"`
+	Message  string            `json:"message"`
+	Msg      string            `json:"msg"`
+	Err      string            `json:"err"`
+	ErrorMsg string            `json:"error_msg"`
 	Header   struct {
 		Message string `json:"message"`
 	} `json:"header"`