Add blank lines to improve code style.

[wangtao2001]

Overview

Spaces have been added to the short-term-memory.mdx example code.

Type of change

Type: Update existing documentation

Checklist

• I have read the contributing guidelines
• I have tested my changes locally using docs dev
• All code examples have been tested and work correctly
• I have used root relative paths for internal links
• I have updated navigation in src/docs.json if needed
• I have gotten approval from the relevant reviewers
• (Internal team members only / optional) I have created a preview deployment using the Create Preview Branch workflow

Additional notes