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.
This commit is contained in: