fix(sui): correct TrustedSignerInfo::expires_at treatment, new tests, refactor

[matej-douro]

Summary

• fixed i64::test_max_positive_magnitude
• split pyth_lazer_tests::test_verify_le_ecdsa_message_untrusted_signer to observe both failures
• fixed TrustedSignerInfo::expires_at vs. clock time, added tests
  • previously, expires_at was incorrectly treated as millis instead of seconds
• added state::expires_at_ms to make conversions more readable
• switched to method calls and indexing in touched code where applicable
• removed unnecessary casts
• other refactoring

How has this been tested?

• Current tests cover my changes
• Added new tests
• Manually tested the code

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