Fix parallel code gen in RT backend

• Properly use Arc<Mutex<_Option<JoinHandle<_, _>>_>> for task parallel calls.
  • Include Arc clones right before opening async closure (for async calls and for fork-joins).
• Make data parallel fork-joins not task parallel by default (can still be outlined for task parallelism).
• Fix edge case in function inlining.

hercules_opt/src/inline.rs

@@ -210,7 +210,11 @@ fn inline_func(
             }
 
             // Finally, delete the call node.
-            edit = edit.replace_all_uses(id, old_id_to_new_id(called_return_data))?;
+            if let Node::Parameter { index } = called_func.nodes[called_return_data.idx()] {
+                edit = edit.replace_all_uses(id, args[index])?;
+            } else {
+                edit = edit.replace_all_uses(id, old_id_to_new_id(called_return_data))?;
+            }
             edit = edit.delete_node(control)?;
             edit = edit.delete_node(id)?;