refactor(executor): optimize payload cloning and streamline SDK translator usage

- Replaced unnecessary `bytes.Clone` calls for `opts.OriginalRequest` throughout executors.
- Introduced intermediate variable `originalPayloadSource` to simplify payload processing.
- Ensured better clarity and structure in request translation logic.

sdk/api/handlers/handlers.go

@@ -377,9 +377,13 @@ func (h *BaseAPIHandler) ExecuteWithAuthManager(ctx context.Context, handlerType
 	}
 	reqMeta := requestExecutionMetadata(ctx)
 	reqMeta[coreexecutor.RequestedModelMetadataKey] = normalizedModel
+	payload := rawJSON
+	if len(payload) == 0 {
+		payload = nil
+	}
 	req := coreexecutor.Request{
 		Model:   normalizedModel,
-		Payload: cloneBytes(rawJSON),
+		Payload: payload,
 	}
 	opts := coreexecutor.Options{
 		Stream:          false,
@@ -416,9 +420,13 @@ func (h *BaseAPIHandler) ExecuteCountWithAuthManager(ctx context.Context, handle
 	}
 	reqMeta := requestExecutionMetadata(ctx)
 	reqMeta[coreexecutor.RequestedModelMetadataKey] = normalizedModel
+	payload := rawJSON
+	if len(payload) == 0 {
+		payload = nil
+	}
 	req := coreexecutor.Request{
 		Model:   normalizedModel,
-		Payload: cloneBytes(rawJSON),
+		Payload: payload,
 	}
 	opts := coreexecutor.Options{
 		Stream:          false,
@@ -458,9 +466,13 @@ func (h *BaseAPIHandler) ExecuteStreamWithAuthManager(ctx context.Context, handl
 	}
 	reqMeta := requestExecutionMetadata(ctx)
 	reqMeta[coreexecutor.RequestedModelMetadataKey] = normalizedModel
+	payload := rawJSON
+	if len(payload) == 0 {
+		payload = nil
+	}
 	req := coreexecutor.Request{
 		Model:   normalizedModel,
-		Payload: cloneBytes(rawJSON),
+		Payload: payload,
 	}
 	opts := coreexecutor.Options{
 		Stream:          true,