Function register_scalar 

pub fn register_scalar<F, T>(
    connection: &Connection,
    options: FunctionOptions,
    callback: F,
) -> Result<()>
where
    F: Fn(&Context<'_>) -> Result<T> + Send + 'static,
    T: SqlFnOutput,

Register a scalar callback on one SQLite connection.

Registration belongs to the connection and lasts until it is closed or the function is explicitly removed.