refactor(predicates): return features instead of bool, add P00/P11 predicates

- Change predicate return type from `bool` to `features list option` to
  carry extracted event data (Summary, Day_start, Multi_day) alongside
  match results
- Add `features` type with Generic_feature_presence, Summary, Day_start,
  Multi_day variants
- Add P00 (has_summary) and P11 (override_events) predicates
- Remove large commented-out icalendar/ptime type definitions
- Refactor main.ml to group events by UID using a Map
- Add get_y_m_d_from_timedesc helper to Utils

bin/remind.ml

@@ -1,3 +1,7 @@
+(*
+  FILE INTERAMENTE GENERATO DA LLM, DA RIVEDERE COMPLETAMENTE
+*)
+
 (** Types for representing Remind events *)
 
 (** Weekday names in Remind format *)