Function record_delivery 

pub async fn record_delivery(
    pool: &SqlitePool,
    id: &str,
    subscription_id: &str,
    event_id: Option<&str>,
    event_type: Option<&str>,
    delivered: bool,
    attempts: i64,
    response_code: Option<i64>,
    error: Option<&str>,
)

Insert one row into the webhook_deliveries ledger. Best-effort: a failure is logged, not fatal.