fix(core): async import emission

This commit fixes async import emissions in the case of lowered args
and lifted resutls.

There were a few bugs to fix:

- AsyncTaskReturn was not being emitted

- Implementation for async imports was not present

Author: vados-cosmonic

crates/core/src/abi.rs

@@ -1093,10 +1093,21 @@ impl<'a, B: Bindgen> Generator<'a, B> {
                 }
 
                 // Emit the function return
-                self.emit(&Instruction::Return {
-                    func,
-                    amt: usize::from(func.result.is_some()),
-                });
+                if async_ {
+                    self.emit(&Instruction::AsyncTaskReturn {
+                        name: &func.name,
+                        params: if func.result.is_some() {
+                            &[WasmType::Pointer]
+                        } else {
+                            &[]
+                        },
+                    });
+                } else {
+                    self.emit(&Instruction::Return {
+                        func,
+                        amt: usize::from(func.result.is_some()),
+                    });
+                }
             }
 
             LiftLower::LiftArgsLowerResults => {
@@ -1134,7 +1145,10 @@ impl<'a, B: Bindgen> Generator<'a, B> {
                     for (param_name, ty) in func.params.iter() {
                         let Some(types) = flat_types(self.resolve, ty, Some(max_flat_params))
                         else {
-                            panic!("failed to flatten types during direct parameter lifting ('{param_name}' in func '{}')", func.name);
+                            panic!(
+                                "failed to flatten types during direct parameter lifting ('{param_name}' in func '{}')",
+                                func.name
+                            );
                         };
                         for _ in 0..types.len() {
                             self.emit(&Instruction::GetArg { nth: offset });