refactor: replace .boxed() streams with Either

This commit replaces `BoxStream`s with streams wrapped by an `Either` to
save an unnecessary allocation (respectively leaving it to client code).

src/api.rs

@@ -2,7 +2,7 @@ use std::borrow::Cow;
 use std::future::Future;
 use std::sync::{Arc, OnceLock};
 
-use futures_util::stream::{BoxStream, Stream, StreamExt as _};
+use futures_util::stream::{Stream, StreamExt as _};
 use reqwest::StatusCode;
 use serde::{Deserialize, Serialize};
 use url::Url;
@@ -213,20 +213,27 @@ impl Client {
         }
     }
 
-    pub fn shorten<'a, S>(&self, urls: S, ordering: Ordering) -> BoxStream<'a, Result<Bitlink>>
+    pub fn shorten<'a, S>(
+        &self,
+        urls: S,
+        ordering: Ordering,
+    ) -> impl Stream<Item = Result<Bitlink>> + 'a
     where
         S: Stream<Item = Url> + Send + 'a,
     {
         let client = Arc::clone(&self.inner);
         let max_concurrent = client.cfg.max_concurrent;
 
         match ordering {
-            Ordering::Ordered => client.shorten_all(urls).buffered(max_concurrent).boxed(),
+            Ordering::Ordered => client
+                .shorten_all(urls)
+                .buffered(max_concurrent)
+                .left_stream(),
 
             Ordering::Unordered => client
                 .shorten_all(urls)
                 .buffer_unordered(max_concurrent)
-                .boxed(),
+                .right_stream(),
         }
     }
 }

src/main.rs

@@ -1,3 +1,5 @@
+use std::pin::pin;
+
 use clap::Parser as _;
 use futures_util::stream::{self, StreamExt as _};
 
@@ -42,12 +44,12 @@ async fn main() {
                 let Some(urls) = io::read_input::<url::Url>() else {
                     return;
                 };
-                urls.map(|url| crash_if_err!(url)).boxed()
+                urls.map(|url| crash_if_err!(url)).left_stream()
             } else {
-                stream::iter(args.urls).boxed()
+                stream::iter(args.urls).right_stream()
             };
 
-            let mut results = client.shorten(urls, args.ordering);
+            let mut results = pin!(client.shorten(urls, args.ordering));
 
             match args.ordering {
                 Ordering::Ordered => {