fix: Move `extern crate alloc` to lib.rs

src/lib.rs

@@ -230,6 +230,8 @@
 #![doc(html_logo_url = "https://async.rs/images/logo--hero.svg")]
 #![recursion_limit = "2048"]
 
+extern crate alloc;
+
 #[macro_use]
 mod utils;
 

src/utils.rs

@@ -1,7 +1,3 @@
-#[cfg(feature = "alloc")]
-extern crate alloc;
-
-#[cfg(feature = "alloc")]
 use alloc::string::String;
 
 /// Calls a function and aborts if it panics.