Promote the window table functions window attribute data type with precision 3

Now the window_start and window_end has a type of a Timestamp with default system precision. But, actually, many DB vendors has default precision as 6 (which is also defined in the SQL standard).

We better promote the precision to 3 because:
1. For windowing, time unit as millisecond is enough
2. Make the precision deterministic instead of overriding by each engine's default one