proposal: time: add constants for DatetimeMilli, DatetimeMicro, and DatetimeNano Formats

[chenmingyong0423]

Problem Description

Currently, the Go time package lacks predefined constants to represent datetime formats with millisecond(e.g., 2006-01-02 15:04:05.000), microsecond(e.g., 2006-01-02 15:04:05.000000), and nanosecond(e.g., 2006-01-02 15:04:05.000000000) precision. This requires developers to manually write format strings when they need to use these datetime formats.

Solution

I propose adding three constants in the time package to represent the "2006-01-02 15:04:05.000", "2006-01-02 15:04:05.000000", and "2006-01-02 15:04:05.000000000" datetime formats, making it convenient for developers to use in their projects.

Example

These constants could be named DatetimeMilli, DatetimeMicro, and DatetimeNano, and developers could use them as follows:

formattedTimeMilli := time.Now().Format(time.DatetimeMilli)
formattedTimeMicro := time.Now().Format(time.DatetimeMicro)
formattedTimeNano := time.Now().Format(time.DatetimeNano)

[seankhliao]

back in #52746 we didn't see we widespread use of such formats, has anything changed in that regard?