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.

Macros that transform test method signature can append
`#[::core::prelude::v1::test]` directly without checking its existence
once they generate valid signature for test method.

Closes frondeus#101.

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

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