[langgraph]: Wrong import for Persistence docs page - Checkpoints section

### Type of issue

issue / bug

### Language

JavaScript

### Description

<img width="697" height="650" alt="Image" src="https://github.com/user-attachments/assets/f4202767-f9ed-4ff9-b4f9-d7c9cd18a2ce" />

Should be `MemorySaver`

also the example is repeated