feat: get timestamp #86

[smallbearrr]

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[peter-jerry-ye-code-review]

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Looking at the git diff, here are potential issues I've noticed:

1. In the now() function, current_second calculation only returns seconds within a minute (0-59) due to % 60. This might be unintended as typically timestamp functions return total seconds since epoch, not just the seconds within the current minute.

2. In the nanosecond calculation (t % 1000 * 1_000_000).to_uint(), there might be precision loss since the calculation assumes t is in milliseconds and converts to nanoseconds. If higher precision is needed, this conversion might not be accurate enough.

3. There's an inconsistency in the type signatures between the implementation (.mbt) and interface (.mbti) files. The implementation specifies UInt64 and UInt return types explicitly, but this level of specificity isn't reflected in the interface file which just shows fn now() -> (UInt64, UInt). It would be good to add documentation in the interface file to match the implementation file's comments.

These observations might or might not be actual problems depending on the specific requirements of your system, but they're worth reviewing.

[peter-jerry-ye]

I think it would be better to keep time library containing purely the algorithm, and leave the system related API in env.