fix: improve compatibility among test proc macros

This pr proposes a generic mechanism among different test proc macros to
avoid to generate multiple `[::core::prelude::v1::test]` on test method.

`proc_macro_attribute` function is fed with tokens after its attribute
and no tokens before it.

Give the above, this pr proposes test proc macros to append newly
generated macros after existing ones. This way, proc macros processed
later can read all macros including generated and handwritten and make
further decisions. Specifically, proc macros can append
`#[::core::prelude::v1::test]` only if it does not exist.

Closes #101.

crates/test-case-core/src/test_case.rs

@@ -99,7 +99,10 @@ impl TestCase {
                 quote! { let _result = super::#item_name(#(#arg_values),*).await; },
             )
         } else {
-            attrs.insert(0, parse_quote! { #[::core::prelude::v1::test] });
+            let test_attr = parse_quote! { #[::core::prelude::v1::test] };
+            if !attrs.iter().any(|attr| *attr == test_attr) {
+                attrs.push(test_attr);
+            }
             (
                 TokenStream2::new(),
                 quote! { let _result = super::#item_name(#(#arg_values),*); },