test: add playground lab to practice

backend/src/utils/math.ts

@@ -0,0 +1,10 @@
+export function myCustomAdd(a: number, b: number): number {
+  return a + b
+}
+
+export function fabonacci(n: number): number {
+  if (n === 1 || n === 2) {
+    return 1
+  }
+  return fabonacci(n - 1) + fabonacci(n - 2)
+}