source_a: 2 users
source_b: 2 users
source_c: 2 users

Merged 4 unique users -> /app/merged_users.parquet
   user_id         name        email created_date    status
0      101     John Doe   john@a.com   2024-01-15    active
1      102   Jane Smith   jane@a.com   2024-02-20  inactive
2      103   Bob Wilson    bob@b.com   2024-03-01      <NA>
3      104  Alice Brown  alice@c.com   2024-04-01      <NA>

3 conflicts -> /app/conflicts.json
