Example: SQL Database Resilience with sql.DB

[cinar]

Add a new example in examples/sql/ demonstrating how to use Resile with the standard library database/sql package. The example should show how to wrap db.QueryContext or db.ExecContext with a Resile policy including retries and a circuit breaker.

Requirements:

• Use resile.Do or resile.DoErr.
• Include a mock database or a simple SQLite setup.
• Add a README.md in the example folder.

This is a good first issue for anyone looking to contribute to Resile!