+ Next month corner case -- it will try to make Feb 31, 2022 then count
+ backwards.
+ >>> base = string_to_datetime("2022/01/31 11:24:51AM-0700")[0]
+ >>> n_timeunits_from_base(1, TimeUnit.MONTHS, base)
+ datetime.datetime(2022, 2, 28, 11, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))
+
+ Last month with the same corner case
+ >>> base = string_to_datetime("2022/03/31 11:24:51AM-0700")[0]
+ >>> n_timeunits_from_base(-1, TimeUnit.MONTHS, base)
+ datetime.datetime(2022, 2, 28, 11, 24, 51, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))
+