fix: correct test descriptions and add EOF newline

[tmdeveloper007]

Closes #491.

Summary of What Has Been Done:
Fixed the crypto.test.ts file based on maintainer feedback:

1. Changed test descriptions from 'should throw on...' to 'should return null on...' since decryptToken returns null on invalid input
2. Added missing EOF newline

Changes Made:

• File: src/lib/crypto.test.ts
• Fixed test descriptions for all 4 invalid input tests
• Added trailing newline

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GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

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