Enhancement: Create Leaderboards access for mods

[EliteMasterEric]

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Issue Checklist

• [x] I have read the Contributing Guide
• [x] I have checked the Issues/Discussions pages to see if my enhancement has already been suggested
• [x] I have properly titled my enhancement

What is your suggestion, and why should it be implemented?

Implement a new LeaderboardsSandboxed class, which grants access to a limited subset of the functions of funkin.api.newgrounds.Leaderboards.

This would allow mods to retrieve scores and other leaderboard data, while allowing API access to be limited to exclude write access.