Fixes for Rust 1.81.0 (#1333)

### What

Fixes for Rust 1.81:

1. Update semver-checks to 0.35.0.

2. Don't use the `extern` function for invoking a contract function when
executing tests.

### Why

1. Semver checks is failing to run on the new version of Rust and needs
updating.

2. Rust 1.81.0 changed the behavior of panics on `extern "C"` functions,
such that panics cannot be caught by
[std::panic::catch_unwind](https://doc.rust-lang.org/std/panic/fn.catch_unwind.html).

Contracts expose their functions as an `extern` function that defaults
to `extern "C"`. The test environment catches panics inside contract
functions and resurfaces them as errors by using catch_unwind.

The solution used was to make it so that the test environment never
calls through the extern function, and instead calls through a
non-extern function that does the same work. This seems like the sanest
way to take away any dependence / relationship between the test
environment and the Rust C-ABI so that any future changes to the C-ABI
don't affect the test environment.

An alternative solution would be to mark the contract function as
`extern "C-unwind"` so that it retained unwind functionality, but that
would continue to bind the SDK test environment to behaviour changes in
extern fns.

In the solution in this change the Abi qualifier `"C"` has been added.
When the Abi qualifier is not specified it defaults to `"C"`, but for
the sake of being explicit and removing any doubt from a reader it is
now specified. The Rust reference confirms that `"C"` is the default:
-
https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier.
   
   More details on this change to Rust 1.81.0 can be found at:
-
https://blog.rust-lang.org/2024/09/05/Rust-1.81.0.html#abort-on-uncaught-panics-in-extern-c-functions
   - rust-lang/rust#74990
    
   Close #1332

.github/workflows/rust.yml

@@ -57,10 +57,10 @@ jobs:
     steps:
     - uses: actions/checkout@v3
     - run: rustup update
-    - uses: stellar/binaries@v24
+    - uses: stellar/binaries@v30
       with:
         name: cargo-semver-checks
-        version: 0.32.0
+        version: 0.35.0
     - run: cargo semver-checks
 
   build-and-test:

soroban-sdk-macros/src/derive_fn.rs

@@ -50,7 +50,7 @@ pub fn derive_pub_fn(
     });
 
     // Prepare the argument inputs.
-    let (wrap_args, wrap_calls): (Vec<_>, Vec<_>) = inputs
+    let (wrap_args, passthrough_calls, wrap_calls): (Vec<_>, Vec<_>, Vec<_>) = inputs
         .iter()
         .skip(if env_input.is_some() { 1 } else { 0 })
         .enumerate()
@@ -78,6 +78,7 @@ pub fn derive_pub_fn(
                     colon_token: Colon::default(),
                     ty: Box::new(Type::Verbatim(quote! { #crate_path::Val })),
                 });
+                let passthrough_call = quote! { #ident };
                 let call = quote! {
                     <_ as #crate_path::unwrap::UnwrapOptimized>::unwrap_optimized(
                         <_ as #crate_path::TryFromValForContractFn<#crate_path::Env, #crate_path::Val>>::try_from_val_for_contract_fn(
@@ -86,11 +87,11 @@ pub fn derive_pub_fn(
                         )
                     )
                 };
-                (arg, call)
+                (arg, passthrough_call, call)
             }
             FnArg::Receiver(_) => {
                 errors.push(Error::new(a.span(), "self argument not supported"));
-                (a.clone(), quote! {})
+                (a.clone(), quote! {}, quote! {})
             }
         })
         .multiunzip();
@@ -132,8 +133,7 @@ pub fn derive_pub_fn(
             use super::*;
 
             #[deprecated(note = #deprecated_note)]
-            #[cfg_attr(target_family = "wasm", export_name = #wrap_export_name)]
-            pub extern fn invoke_raw(env: #crate_path::Env, #(#wrap_args),*) -> #crate_path::Val {
+            pub fn invoke_raw(env: #crate_path::Env, #(#wrap_args),*) -> #crate_path::Val {
                 #use_trait;
                 <_ as #crate_path::IntoVal<#crate_path::Env, #crate_path::Val>>::into_val(
                     #[allow(deprecated)]
@@ -154,6 +154,13 @@ pub fn derive_pub_fn(
                 invoke_raw(env, #(#slice_args),*)
             }
 
+            #[deprecated(note = #deprecated_note)]
+            #[cfg_attr(target_family = "wasm", export_name = #wrap_export_name)]
+            pub extern "C" fn invoke_raw_extern(env: #crate_path::Env, #(#wrap_args),*) -> #crate_path::Val {
+                #[allow(deprecated)]
+                invoke_raw(env, #(#passthrough_calls),*)
+            }
+
             use super::*;
         }
     })