feat: Add section on bn128 curve termination and memory management in proofs.mdx

[crStiv]

Description

This PR adds a new section to the proofs.mdx documentation covering best practices around memory management when working with the bn128 elliptic curve in Semaphore. Specifically, it explains why explicit curve termination is necessary in Node.js environments and how to implement it properly using ffjavascript.

The addition includes:

• A detailed explanation of curve termination and potential memory leaks
• Usage examples for both application and test environments
• Best practices to ensure safe and clean memory handling
• Code snippets that follow Semaphore conventions

Related Issue(s)

Fixes #897

Checklist

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have run yarn format and yarn lint without getting any errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Important

We do not accept pull requests for minor grammatical fixes (e.g., correcting typos, rewording sentences) or for fixing broken links, unless they significantly improve clarity or functionality. These contributions, while appreciated, are not a priority for merging. If you notice any of these issues, please create a GitHub Issue to report them so they can be properly tracked and addressed.