examples/value_list: return Result

There were a lot of unwraps in this example, which are
not encouraged and introduce some noise.

Let's return a Result from main and propagate the errors.

examples/value_list.rs

@@ -1,23 +1,23 @@
+use anyhow::Result;
 use scylla::{Session, SessionBuilder};
 use std::env;
 
 #[tokio::main]
-async fn main() {
+async fn main() -> Result<()> {
     let uri = env::var("SCYLLA_URI").unwrap_or_else(|_| "127.0.0.1:9042".to_string());
 
     println!("Connecting to {} ...", uri);
 
-    let session: Session = SessionBuilder::new().known_node(uri).build().await.unwrap();
+    let session: Session = SessionBuilder::new().known_node(uri).build().await?;
 
-    session.query_unpaged("CREATE KEYSPACE IF NOT EXISTS examples_ks WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'replication_factor' : 1}", &[]).await.unwrap();
+    session.query_unpaged("CREATE KEYSPACE IF NOT EXISTS examples_ks WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'replication_factor' : 1}", &[]).await?;
 
     session
         .query_unpaged(
             "CREATE TABLE IF NOT EXISTS examples_ks.my_type (k int, my text, primary key (k))",
             &[],
         )
-        .await
-        .unwrap();
+        .await?;
 
     #[derive(scylla::SerializeRow)]
     struct MyType<'a> {
@@ -35,8 +35,7 @@ async fn main() {
             "INSERT INTO examples_ks.my_type (k, my) VALUES (?, ?)",
             to_insert,
         )
-        .await
-        .unwrap();
+        .await?;
 
     // You can also use type generics:
     #[derive(scylla::SerializeRow)]
@@ -55,13 +54,13 @@ async fn main() {
             "INSERT INTO examples_ks.my_type (k, my) VALUES (?, ?)",
             to_insert_2,
         )
-        .await
-        .unwrap();
+        .await?;
 
     let q = session
         .query_unpaged("SELECT * FROM examples_ks.my_type", &[])
-        .await
-        .unwrap();
+        .await?;
 
     println!("Q: {:?}", q.rows);
+
+    Ok(())
 }