Function builtin_as_posixct 

fn builtin_as_posixct(
    args: &[RValue],
    named: &[(String, RValue)],
) -> Result<RValue, RError>

Convert a character string or numeric value to a POSIXct date-time.

@param x character string, numeric (seconds since epoch), or POSIXct to convert @param tz timezone name (default: UTC for parsing, system for display) @return a POSIXct object