Function open 

pub async fn open(db_url: &str) -> Result<Connection>

Opens db_url and applies the migrations.

• file:./data/auth.db or a bare path: a local file, parent folders created
• :memory:: ephemeral
• libsql://…, http://…, https://…: remote Turso, authenticated by PACENOTES_DB_AUTH_TOKEN, an environment variable so it stays out of the process list