qe: Fix timeout errors (#4641)

* qe: Fix timeout errors

Problem: we awaited spawned future immediately, which kind of makes
spawn useless, effecctively serializing batch requests instead of
executing them in parallel. Affects only the batches that could not be
compated into a single query.

I struggled to reproduce the error in engine's test suite. I suggest we
test it in client instead.

Fix prisma/prisma#22610

* Fix wasm

* Use spawn_local for WASM branch

* Address more review comments

libs/crosstarget-utils/src/native/spawn.rs

@@ -1,11 +1,12 @@
+use futures::TryFutureExt;
 use std::future::Future;
 
 use crate::common::SpawnError;
 
-pub async fn spawn_if_possible<F>(future: F) -> Result<F::Output, SpawnError>
+pub fn spawn_if_possible<F>(future: F) -> impl Future<Output = Result<F::Output, SpawnError>>
 where
     F: Future + 'static + Send,
     F::Output: Send + 'static,
 {
-    tokio::spawn(future).await.map_err(|_| SpawnError)
+    tokio::spawn(future).map_err(|_| SpawnError)
 }

libs/crosstarget-utils/src/wasm/spawn.rs

@@ -1,10 +1,20 @@
 use std::future::Future;
 
+use futures::TryFutureExt;
+use tokio::sync::oneshot;
+use wasm_bindgen_futures::spawn_local;
+
 use crate::common::SpawnError;
 
-pub async fn spawn_if_possible<F>(future: F) -> Result<F::Output, SpawnError>
+pub fn spawn_if_possible<F>(future: F) -> impl Future<Output = Result<F::Output, SpawnError>>
 where
     F: Future + 'static,
 {
-    Ok(future.await)
+    let (sx, rx) = oneshot::channel();
+    spawn_local(async move {
+        let result = future.await;
+        _ = sx.send(result);
+    });
+
+    rx.map_err(|_| SpawnError)
 }