sum_tree: Replace rayon with futures (#41586)

Release Notes:

- N/A *or* Added/Fixed/Improved ...

Co-authored by: Kate <kate@zed.dev>

crates/extension_host/src/extension_host.rs

@@ -1468,6 +1468,7 @@ impl ExtensionStore {
         let extensions_dir = self.installed_dir.clone();
         let index_path = self.index_path.clone();
         let proxy = self.proxy.clone();
+        let executor = cx.background_executor().clone();
         cx.background_spawn(async move {
             let start_time = Instant::now();
             let mut index = ExtensionIndex::default();
@@ -1501,10 +1502,14 @@ impl ExtensionStore {
             }
 
             if let Ok(index_json) = serde_json::to_string_pretty(&index) {
-                fs.save(&index_path, &index_json.as_str().into(), Default::default())
-                    .await
-                    .context("failed to save extension index")
-                    .log_err();
+                fs.save(
+                    &index_path,
+                    &Rope::from_str(&index_json, &executor),
+                    Default::default(),
+                )
+                .await
+                .context("failed to save extension index")
+                .log_err();
             }
 
             log::info!("rebuilt extension index in {:?}", start_time.elapsed());
@@ -1671,7 +1676,7 @@ impl ExtensionStore {
                 let manifest_toml = toml::to_string(&loaded_extension.manifest)?;
                 fs.save(
                     &tmp_dir.join(EXTENSION_TOML),
-                    &Rope::from(manifest_toml),
+                    &Rope::from_str_small(&manifest_toml),
                     language::LineEnding::Unix,
                 )
                 .await?;