update usage of isodatetime methods

[wxtim]

Use new names of Isodatetime interfaces.

[MetRonnie]

I spotted another needed fix:

diff --git a/metomi/rose/date.py b/metomi/rose/date.py
index dd4511c3..de9cf31c 100644
--- a/metomi/rose/date.py
+++ b/metomi/rose/date.py
@@ -302,8 +302,7 @@ class RoseDateTimeOperator:
     @classmethod
     def get_datetime_strftime(cls, time_point, print_format):
         """Use the datetime library's strftime as a fallback."""
-        calendar_date = time_point.copy().to_calendar_date()
-        year, month, day = calendar_date.get_calendar_date()
+        year, month, day = time_point.get_calendar_date()
         hour, minute, second = time_point.get_hour_minute_second()
         microsecond = int(1.0e6 * (second - int(second)))
         hour = int(hour)

Also, I think we should specify this version range, because we rely on the 3.x API:

diff --git a/setup.cfg b/setup.cfg
index d89a5b80..40e9fe36 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -53,7 +53,7 @@ install_requires =
     aiofiles
     jinja2>=2.10.1
     ldap3
-    metomi-isodatetime
+    metomi-isodatetime==3.*
     psutil>=5.6.0
     requests
     sqlalchemy

Possibly even 3.0.*? (Update from team catchup: whatever)

[MetRonnie]

Good spot about the epoch