Fix build with 1.81

As of 1.81, `stringify` appears to always insert spaces between tokens,
resulting in type names like `std :: io :: File`. Switching to `concat`
avoids this issue.

Due to the use of `local_inner_macros`, we fully qualify `concat` and
`stringify` in the definition of `field_decl_inner`.

vm/src/api/mac.rs

@@ -177,7 +177,7 @@ macro_rules! field_decl_inner {
         record_field_inner_struct!{ $field $($suffix)* }
         impl $crate::api::record::Field for last_ident!($field $($suffix)*) {
             fn name() -> &'static str {
-                stringify_inner!($field $( :: $suffix)* )
+                ::std::concat!(::std::stringify!($field), $("::", ::std::stringify!($suffix)),*)
             }
             fn args() -> &'static [&'static str] {
                 &[$(stringify_inner!($args)),*]