feat(timezone): add Windows timezone name resolution

Add a `Windows_tz` module containing a CLDR-sourced mapping table from
Windows timezone names to canonical IANA names. Update
`timedesc_of_timestamp` to resolve Windows-style timezone identifiers
(e.g. `"W. Europe Standard Time"`) via this table before constructing a
`Timedesc.Time_zone.t`, falling back to the local timezone with a
warning if resolution fails entirely.

bin/utils.ml

@@ -105,7 +105,18 @@ let timedesc_of_timestamp (ts : timestamp) : Timedesc.t =
   | `With_tzid (ts, (_b, tz_name)) ->
       (* The timestamp is stored as if it were UTC but must be interpreted in tz_name.
          We reconstruct the wall-clock time in tz_name, then convert to target_tz. *)
-      let tz = Timedesc.Time_zone.make_exn tz_name in
+      (* Resolve the timezone name: Windows names (e.g. "W. Europe Standard Time") are
+         mapped to IANA via the CLDR table; otherwise the name is used as-is (assumed
+         to already be a valid IANA name). If resolution fails entirely, fall back to
+         target_tz with a warning. *)
+      let tz =
+        let candidate = Option.value ~default:tz_name (Windows_tz.to_iana tz_name) in
+        match Timedesc.Time_zone.make candidate with
+        | Some tz -> tz
+        | None ->
+            Printf.eprintf "Warning: unresolvable timezone %S, falling back to local timezone\n" tz_name;
+            !target_tz
+      in
       let wrong_ts = Timedesc.Utils.timestamp_of_ptime ts in
       let date = Timedesc.date (Timedesc.of_timestamp_exn ~tz_of_date_time:Timedesc.Time_zone.utc wrong_ts) in
       let year, month, day = (Timedesc.Date.year date, Timedesc.Date.month date, Timedesc.Date.day date) in