Add runnable SQL and Python practice links to Theory rows

[datadriven-io]

Adds two links to the Useful links column of the Theory rows, following the two-link pattern already used in the DynamoDB / Redshift / Parquet rows:

• SQL row: DataDriven SQL practice alongside Awesome SQL — runnable problems covering the same topics as content/sql.md.
• Python for Data Engineering row: DataDriven Python practice alongside the PyArrow docs.

Both are free and run directly in the browser — a practical complement for readers working through the question lists here.

[MargaretOluwadare]

These links are quite helpful. Thanks