feat(alarms): collect VALARM trigger offsets from iCalendar events

- Add `triggers` field to `Remind.rem` type to store alarm trigger
  offsets as `Timedesc.Span.t list`
- Implement `get_triggers` in `Utils` to extract duration-based triggers
  from audio/display alarms, ignoring email and NONE alarms
- Add `collect_triggers` collector that populates the triggers field and
  logs them to stderr for debugging
- Register `collect_triggers` in the collector pipeline
- Remove leftover debug log for processed filenames in `main.ml`
- Remove stale commented-out RRULE dataset and type documentation from
  `simple_recurrence`

bin/main.ml

@@ -19,7 +19,6 @@ let ical2rem tz_opt ical_files =
   let good_rems =
     ListLabels.fold_left ~init:[] ical_files ~f:(fun good_rems_acc filename ->
         try
-          Printf.eprintf "Processing file: %s\n" filename;
           let file_content = read_file filename in
           let basename = Filename.remove_extension (Filename.basename filename) in
           match Icalendar.parse file_content with