refactor: remove remind_sync wrapper library and inline utilities

The `remind_sync` library was acting as a thin re-export layer. This
commit removes it entirely and moves the only non-trivial utility
(`show_error` for `Timedesc.Date.Ymd.error`) directly into
`bin/utils.ml`. Dead `[@@deriving show]` annotations on `rem`,
`week_first_day`, and `error` types are also removed.

bin/dune

@@ -5,7 +5,6 @@
  (preprocess
   (pps ppx_deriving.show))
  (libraries
-  remind_sync
   cmdliner
   icalendar
   timedesc-tzdb.full

bin/eventPredicates.ml

@@ -1,4 +1,3 @@
-open Remind_sync
 open Icalendar
 open Utils
 
@@ -148,11 +147,9 @@ open Utils
     priorita: Quando serve
 *)
 
-type error = Invalid_date of string | Skip [@@deriving show]
-
-let invalid_date s e =
-  Error (Invalid_date (spf "Invalid date: %s, error: %s" s (Remind_sync.Timedesc.Date.Ymd.show_error e)))
+type error = Invalid_date of string | Skip
 
+let invalid_date s e = Error (Invalid_date (spf "Invalid date: %s, error: %s" s (show_error e)))
 let skip = Error Skip
 
 type collector = Remind.rem -> event -> (Remind.rem, error) result

bin/main.ml

@@ -1,4 +1,3 @@
-open Remind_sync
 module Map = MoreLabels.Map.Make (String)
 
 (*

bin/remind.ml

@@ -1,7 +1,6 @@
-open Remind_sync
 open Utils
 
-type week_first_day = [ `Sunday | `Monday ] [@@deriving show]
+type week_first_day = [ `Sunday | `Monday ]
 
 type simple_weekly = {
   count_or_until : Icalendar.count_or_until option;
@@ -9,7 +8,6 @@ type simple_weekly = {
   byday : Icalendar.weekday list;
   week_start : week_first_day option;  (** First day of the week for weekly recurrence *)
 }
-[@@deriving show]
 (** A simple weekly REM command *)
 
 type rem = {
@@ -26,7 +24,6 @@ type rem = {
       *)
   exdate : Icalendar.date_or_datetime list;  (** List of excluded dates for recurring events *)
 }
-[@@deriving show]
 (** A complete REM command *)
 
 let empty =

bin/utils.ml

@@ -1,8 +1,14 @@
-open Remind_sync
 open Icalendar
 
 type months = Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
 
+let show_error (e : Timedesc.Date.Ymd.error) : string =
+  match e with
+  | `Does_not_exist -> "Date does not exist"
+  | `Invalid_year y -> Printf.sprintf "Invalid year: %d" y
+  | `Invalid_month m -> Printf.sprintf "Invalid month: %d" m
+  | `Invalid_day d -> Printf.sprintf "Invalid day: %d" d
+
 let string_of_weekday = function
   | `Monday -> "Mon"
   | `Tuesday -> "Tue"