….utc_now

Instead of calling DateTime.utc_now and then truncating the result with
DateTime.truncate/2, it's more efficient (and less code) to just pass a
time unit indicating the desired precision to DateTime.utc_now directly.

Dito for NaiveDateTime.

I believe this refactoring is universally plausible, so let's enable it
by default.

Co-authored-by: René Föhring <[email protected]>

Co-authored-by: René Föhring <[email protected]>

This should be a quote from the source code,
Credo.Check.add_column_if_missing/5 relies on this to calculate the
column value for the issue.

The `line_no` value should be the line where the `trigger` appears, i.e.
we should be using the meta information of the `truncate` AST node here.