refactor: improve time and date functions

[ugol]

• nowsub and nowadd with durations as parameters instead of ms
• datesub and dateadd (same but starting from a date)

using different dateformats to decide output

[paoven]

• It would be very helpful allowing timestamp generation functions like now_add, now_sub, just_passed to take delta parameter value as a duration, something like {{now_sub '5s'}}
• Proposing to emit the mentioned timestamp functions output value as an int64/long representing the number of seconds/milliseconds/microseconds from January 1st, 1970 UTC. Desired epoch precision could be taken as an input parameter (defaulting to ms), something like {{just_passed '5s' 'ms'}}
  • this allows end user choosing the desired precision
  • in the case end user needs to format the epoch to a date, it can always do this in the client application. Eventually I propose to consider extending jr functions with a date formatting function which takes in input an epoch and a date format:
    • {{date_format '1727695554' 'RFC1123'}} which would output 'Mon, 30 Sep 2024 13:26:30 CEST'