enable connection pools for sqlite

Connecting is reasonably expensive because the spatialite extension
needs to be loaded. Disable pooling for tests because there is some
memory leak when quickly opening and closing QueuePools with sqlite
connections.

test/python/api/conftest.py

@@ -198,7 +198,8 @@ def frontend(request, event_loop, tmp_path):
                                                                  db, options))
             return napi.NominatimAPI(Path('/invalid'),
                                      {'NOMINATIM_DATABASE_DSN': f"sqlite:dbname={db}",
-                                      'NOMINATIM_USE_US_TIGER_DATA': 'yes'})
+                                      'NOMINATIM_USE_US_TIGER_DATA': 'yes',
+                                      'NOMINATIM_API_POOL_SIZE': '0'})
     elif request.param == 'postgres_db':
         def mkapi(apiobj, options=None):
             return apiobj.api