when a country is in the results, restrict further searches to places

A country search result usually comes with a very high importance.
As a result only other very well known places will show up together
with country results and that means only places with lower address
ranks. Name searches for country names tend to yield a lot of POI
results because the country name is part of the name
(think "embassy of Sweden"). By excluding POIs from further searches,
the search is sped up quite a bit.

nominatim/api/search/db_searches.py

@@ -484,7 +484,14 @@ async def lookup(self, conn: SearchConnection,
             result.bbox = Bbox.from_wkb(row.bbox)
             results.append(result)
 
-        return results or await self.lookup_in_country_table(conn, details)
+        if not results:
+            results = await self.lookup_in_country_table(conn, details)
+
+        if results:
+            details.min_rank = min(5, details.max_rank)
+            details.max_rank = min(25, details.max_rank)
+
+        return results
 
 
     async def lookup_in_country_table(self, conn: SearchConnection,