fix(data_builder): clear weather cache in after block

If build_packet_data raises, the :weather_callsigns_cache process-dict
entry would stick around and poison subsequent unrelated calls on the
same LiveView process. Wrap the building pass in try/after so the key
is always removed.

lib/aprsme_web/live/map_live/data_builder.ex

@@ -43,16 +43,19 @@ defmodule AprsmeWeb.MapLive.DataBuilder do
     weather_set = Aprsme.Packets.weather_callsigns(callsigns)
     Process.put(:weather_callsigns_cache, weather_set)
 
-    result =
+    # try/after so the cache is cleared even if packet building raises —
+    # otherwise a leftover :weather_callsigns_cache entry would poison
+    # subsequent calls on the same LiveView process.
+    try do
       packets_map
       |> Enum.map(fn {_callsign, packet} ->
         build_packet_data(packet, is_most_recent, locale)
       end)
       |> Enum.filter(& &1)
       |> deduplicate_by_callsign_group()
-
-    Process.delete(:weather_callsigns_cache)
-    result
+    after
+      Process.delete(:weather_callsigns_cache)
+    end
   end
 
   @doc """