Move tests from timestamp.rs to sqllogictest 'timestamps.slt'

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Describe the solution you'd like
Move unit tests from timestamp.rs to sqllogictest 'timestamps.slt', perhaps not tests are suitable to be moved, but we need to take care on those which are.

Describe alternatives you've considered
Not doing this
Additional context
Agreed on #5140 (comment)