chore: Consistently use anyhow::Result for example main fn's

When an `Err` is propagated out of `main`, it will be printed using
`Debug`, which is much easier to read in anyhow::Error's case. See also
https://docs.rs/anyhow/latest/anyhow/struct.Error.html#display-representations

crates/matrix-sdk/examples/cross_signing_bootstrap.rs

@@ -72,7 +72,7 @@ async fn login(
 }
 
 #[tokio::main]
-async fn main() -> Result<(), matrix_sdk::Error> {
+async fn main() -> anyhow::Result<()> {
     tracing_subscriber::fmt::init();
 
     let (homeserver_url, username, password) =
@@ -87,5 +87,7 @@ async fn main() -> Result<(), matrix_sdk::Error> {
             }
         };
 
-    login(homeserver_url, &username, &password).await
+    login(homeserver_url, &username, &password).await?;
+
+    Ok(())
 }

crates/matrix-sdk/examples/emoji_verification.rs

@@ -201,7 +201,7 @@ async fn login(
 }
 
 #[tokio::main]
-async fn main() -> Result<(), matrix_sdk::Error> {
+async fn main() -> anyhow::Result<()> {
     tracing_subscriber::fmt::init();
 
     let (homeserver_url, username, password) =
@@ -216,5 +216,7 @@ async fn main() -> Result<(), matrix_sdk::Error> {
             }
         };
 
-    login(homeserver_url, &username, &password).await
+    login(homeserver_url, &username, &password).await?;
+
+    Ok(())
 }

crates/matrix-sdk/examples/get_profiles.rs

@@ -45,7 +45,7 @@ async fn login(
 }
 
 #[tokio::main]
-async fn main() -> Result<(), matrix_sdk::Error> {
+async fn main() -> anyhow::Result<()> {
     tracing_subscriber::fmt::init();
 
     let (homeserver_url, username, password) =

crates/matrix-sdk/examples/image_bot.rs

@@ -74,7 +74,7 @@ async fn login_and_sync(
 }
 
 #[tokio::main]
-async fn main() -> Result<(), matrix_sdk::Error> {
+async fn main() -> anyhow::Result<()> {
     tracing_subscriber::fmt::init();
     let (homeserver_url, username, password, image_path) =
         match (env::args().nth(1), env::args().nth(2), env::args().nth(3), env::args().nth(4)) {

crates/matrix-sdk/examples/login.rs

@@ -47,7 +47,7 @@ async fn login(
 }
 
 #[tokio::main]
-async fn main() -> Result<(), matrix_sdk::Error> {
+async fn main() -> anyhow::Result<()> {
     tracing_subscriber::fmt::init();
 
     let (homeserver_url, username, password) =
@@ -62,5 +62,7 @@ async fn main() -> Result<(), matrix_sdk::Error> {
             }
         };
 
-    login(homeserver_url, &username, &password).await
+    login(homeserver_url, &username, &password).await?;
+
+    Ok(())
 }

crates/matrix-sdk/examples/timeline.rs

@@ -56,7 +56,7 @@ async fn print_timeline(room: Room) {
 }
 
 #[tokio::main]
-async fn main() -> Result<(), matrix_sdk::Error> {
+async fn main() -> anyhow::Result<()> {
     tracing_subscriber::fmt::init();
 
     let (homeserver_url, username, password, room_id) =