Add unit tests for the pagination cursor encoder and decoder round-tripping without data loss

[Chucks1093]

Summary

The cursor-based pagination system encodes a database row ID and sort value into an opaque cursor string and decodes it on the next request. Unit tests should confirm the encode→decode round-trip is lossless for all supported field types.

Scope

• Test encoding and decoding a cursor with an integer ID and timestamp sort value
• Test encoding and decoding a cursor with a string ID and numeric sort value
• Test that a tampered cursor string (base64 modified mid-string) throws InvalidCursor
• Test that an empty string cursor throws InvalidCursor
• Assert decoded values are strictly equal (not just loosely equal) to the originals

Acceptance Criteria

• Integer ID and timestamp round-trips without data loss
• String ID and numeric sort value round-trips correctly
• Tampered cursor throws InvalidCursor
• Empty string cursor throws InvalidCursor
• Decoded values strictly equal originals

ETA: 12 hours

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[supreme2580]

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[Akpolo]

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Hi Maintainer,

I'd like to work on this issue. I'm a full-stack developer with experience in JavaScript, Python, TypeScript, and Rust, and a history of contributing to open-source projects.

I've reviewed the scope and can deliver a solid implementation within 24 hours of being assigned. Happy to share past work if helpful.

Thanks for considering me!

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