macros, vm, bytecode: add #[handler] await-style primop macro

fix-macros/Cargo.toml

@@ -9,7 +9,7 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0"
 quote = "1.0"
-syn = { version = "3.0", features = ["full", "visit-mut"] }
+syn = { version = "3.0", features = ["full", "visit", "visit-mut"] }
 
 [lints]
 workspace = true

fix-macros/src/lib.rs

@@ -1,5 +1,15 @@
 extern crate proc_macro;
 
+mod handler;
+
+#[proc_macro_attribute]
+pub fn handler(
+    attr: proc_macro::TokenStream,
+    item: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    handler::handler(attr.into(), item.into()).into()
+}
+
 // Adapted from `__unelide_lifetimes` in `gc-arena-derive`.
 // Licensed under the MIT license.
 // See: https://github.com/kyren/gc-arena