fix(napi): return the join handle when spawning a tokio task. (#1351)

we need this to be able to safely drop an struct,
that makes use of an async task.
the drop function needs to be able to call `.abort()`
on the join handle to avoid memory corruption and undefined bahviour.

crates/napi/src/tokio_runtime.rs

@@ -52,11 +52,15 @@ pub unsafe extern "C" fn shutdown_tokio_rt(arg: *mut c_void) {
   }
 }
 
-pub fn spawn<F>(fut: F)
+/// Spawns a future onto the Tokio runtime.
+///
+/// Depending on where you use it, you should await or abort the future in your drop function.
+/// To avoid undefined behavior and memory corruptions.
+pub fn spawn<F>(fut: F) -> tokio::task::JoinHandle<F::Output>
 where
   F: 'static + Send + Future<Output = ()>,
 {
-  RT.0.spawn(fut);
+  RT.0.spawn(fut)
 }
 
 /// Runs a future to completion