add new functionality and improve backend server structure

- Enhance server functionality and optimize backend code
- Add multi-database support (PostgreSQL, MySQL, SQLite)

server/core_backend-server/tools/subscriptions/message.go

@@ -0,0 +1,37 @@
+package subscriptions
+
+import (
+	"io"
+)
+
+// Message defines a client's channel data.
+type Message struct {
+	Name string `json:"name"`
+	Data []byte `json:"data"`
+}
+
+// WriteSSE writes the current message in a SSE format into the provided writer.
+//
+// For example, writing to a router.Event:
+//
+//	m := Message{Name: "users/create", Data: []byte{...}}
+//	m.WriteSSE(e.Response, "yourEventId")
+//	e.Flush()
+func (m *Message) WriteSSE(w io.Writer, eventId string) error {
+	parts := [][]byte{
+		[]byte("id:" + eventId + "\n"),
+		[]byte("event:" + m.Name + "\n"),
+		[]byte("data:"),
+		m.Data,
+		[]byte("\n\n"),
+	}
+
+	for _, part := range parts {
+		_, err := w.Write(part)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}