test bounded 1 MiB response behavior on keys/peers pages

[GianIac]

If you'd like to help with Numax, this is a great place to start, thank you so much for taking a look !

Add tests that explicitly validate bounded JSON page behavior near the 1 MiB response limit.

Why

The API intentionally bounds page responses and updates next_cursor when truncating.
This is important behavior that deserves dedicated regression coverage.

Scope

• in crates/nx-api/src/routes.rs tests:
  • add/extend scenarios for large keys pages
  • add/extend scenarios for large peers pages
  • verify response stays within limit and pagination remains contract-safe
• no endpoint contract changes

Done when

• tests confirm bounded responses do not exceed limit
• truncation still returns coherent items and next_cursor
• all nx-api tests pass

Notes

Please prioritize deterministic tests over huge random payloads.

Thanks again for considering contributing to Numax.