test(auth): expand auth flow tests with comprehensive edge cases

[Ndifreke000]

• Add nonce generation and expiry tests (5 tests)

  • Unique nonce generation
  • Timestamp and expiry validation
  • Expired nonce rejection
  • Auto-delete after TTL
  • Prevent nonce reuse across public keys

• Add valid/invalid signature login tests (4 tests)

  • Accept valid signature from correct keypair
  • Reject signature from wrong keypair
  • Reject malformed signature
  • Reject signature for tampered message

• Add token refresh and rotation tests (5 tests)

  • Generate new tokens on refresh
  • Rotate session and invalidate old token
  • Reject expired refresh token
  • Reject refresh token used as access token
  • Maintain user session count during rotation

• Add logout and session cleanup tests (5 tests)

  • Delete single session on logout
  • Delete all user sessions on logout all
  • Blacklist token on logout
  • Remove blacklisted token after TTL
  • Clean up user session set on delete all

• Add concurrent session limits tests (6 tests)

  • Track multiple concurrent sessions
  • Retrieve all active sessions for user
  • Enforce session limit by deleting oldest
  • Handle concurrent session creation race condition
  • Clean up stale session references

Total: 33 tests passing (25 new tests added)

Closes #133

[Ndifreke000]

@GoSTEAN but i did not touch contract, why is it failing??