refactor: Replace length/1 with empty list comparison

Replace expensive length/1 calls with direct list comparison
to fix Credo warnings about performance

test/mv/membership/import/member_csv_test.exs

@@ -404,7 +404,7 @@ defmodule Mv.Membership.Import.MemberCSVTest do
 
       assert chunk_result.inserted == 0
       assert chunk_result.failed == 10
-      assert length(chunk_result.errors) == 0
+      assert chunk_result.errors == []
     end
 
     test "error capping with mixed success and failure" do