refactor: rename project from remind_sync to ical2rem

- Rename executable public_name and package name from remind_sync to
  ical2rem
- Update dune-project with new name, source URI, maintainer, synopsis,
  description, and tags
- Add dune-build-info dependency and use Build_info to generate the
  version string at build time instead of the %%VERSION%% placeholder
- Add pinned dependencies to ical2rem.opam
- Remove remind_sync.opam
- Bump dune lang version from 3.20 to 3.23

ical2rem.opam

@@ -0,0 +1,38 @@
+# This file is generated by dune, edit dune-project instead
+opam-version: "2.0"
+synopsis: "Convert iCalendar (.ics) files to Remind (.rem) format"
+description:
+  "ical2rem reads iCalendar (.ics) files and produces reminders in the Remind format. It handles recurring events, exceptions (EXDATE/RECURRENCE-ID), alarms (VALARM), timezones, and Windows timezone names."
+maintainer: ["Paolo Donadeo <paolo@donadeo.net>"]
+authors: ["Paolo Donadeo <paolo@donadeo.net>"]
+license: "MIT"
+tags: ["icalendar" "remind" "calendar" "ics" "rem" "converter"]
+doc: "https://git.donadeo.net/pdonadeo/ical2rem"
+depends: [
+  "ocaml" {= "5.4.1"}
+  "timedesc" {= "3.1.0"}
+  "timedesc-tzdb" {= "3.1.0"}
+  "timedesc-tzlocal" {= "3.1.0"}
+  "ppx_deriving" {= "6.1.1"}
+  "icalendar" {= "0.1.13"}
+  "dune" {>= "3.23" & dev & = "3.23.1"}
+  "ocamlformat" {dev & = "0.29.0"}
+  "ocaml-lsp-server" {dev & = "1.26.0"}
+  "odoc" {with-doc}
+]
+build: [
+  ["dune" "subst"] {dev}
+  [
+    "dune"
+    "build"
+    "-p"
+    name
+    "-j"
+    jobs
+    "@install"
+    "@runtest" {with-test}
+    "@doc" {with-doc}
+  ]
+]
+dev-repo: "https://git.donadeo.net/pdonadeo/ical2rem"
+x-maintenance-intent: ["(latest)"]