Problems importing large ical files

Follow-up to !12 (comment 42802).

• Beyond a certain size, the secondary instance from which the import command is run fails with a warning of this type:

  ** (orage:42661): WARNING **: 12:01:39.791: import failed file=ical-file.ics

  However, the import continues on the primary instance, and may finish normally soon after if the file is not too large.
  This could be fixed along with #4 (closed), depending on the APIs used to replace dbus-glib.
• There is probably also a performance issue: all else being equal, a 7,600 line ical file that imports in about 30 seconds in Thunderbird 91.6.1, imports in about two minutes in Orage.