add basic scheduler

internal/utilities/singleton.go

@@ -0,0 +1,25 @@
+package utilities
+
+import (
+	"fmt"
+	"sync"
+)
+
+func Singleton[T any](init func() (T, error)) func() T {
+	var (
+		once sync.Once
+		t    T
+	)
+
+	return func() T {
+		once.Do(func() {
+			var err error
+			t, err = init()
+			if err != nil {
+				panic(fmt.Sprintf("creating %T failed: %s", t, err))
+			}
+		})
+
+		return t
+	}
+}