Demo: batch import and timing comparison

Step by step

1. Create the product table with schema.sql in local PostgreSQL.
2. Read a 10,000-line CSV into a list of records.
3. Insert row by row with auto-commit on; time it with System.nanoTime().
4. Planned mistake: open a new DriverManager connection inside the loop; show how slow it gets, then switch to a pooled DataSource.
5. Rewrite with addBatch/executeBatch in chunks of 500 and one commit per chunk; time again.
6. Compare the two numbers and confirm all rows arrived with select count(*).