feat: initial implementation of iCalendar to Remind converter

- Add project scaffolding (dune, dune-project, opam, .ocamlformat)
- Implement basic parsing and handling of iCalendar events
- Add event predicates for common event types (all-day, timed,
  recurrence, exceptions)
- Add transformation logic to map iCalendar events to Remind format
  (stub implementation)
- Provide utilities for extracting event details and converting
  dates/times
- Set up executable entrypoint and command-line interface using Cmdliner
- Include Remind event type definitions and helpers

bin/main.ml

@@ -0,0 +1,34 @@
+let ical2rem ical_file =
+  let ic = open_in ical_file in
+  let n = in_channel_length ic in
+  let s = Bytes.create n in
+  really_input ic s 0 n;
+  close_in ic;
+  let cal_or_error = Icalendar.parse (Bytes.unsafe_to_string s) in
+  match cal_or_error with
+  | Error e -> prerr_endline ("Error parsing iCalendar file: " ^ e)
+  | Ok (_, components) -> begin
+    let events = ref 0 in
+    List.iter
+      (fun comp ->
+        match comp with
+        | `Event event ->
+          events := !events + 1;
+          let uid = Utils.get_uid event in
+          Printf.printf "󰧓 ⇒ UID: %s\n" uid;
+          Printf.printf "%s\n\n\n" (Icalendar.show_component comp)
+        | _ -> () (* Ignore non-event components *))
+      components;
+    Printf.printf "\nEvents: %d\n" !events;
+    let events =
+      List.filter_map
+        (function
+          | `Event ev -> Some ev
+          | _ -> None)
+        components
+    in
+    let _reminders = List.map EventTransformer.remind_of_event events in
+    ()
+  end
+
+let () = if !Sys.interactive then () else exit (CommandLine.main ical2rem)