fix: #[no_mangle] error in Rust 2024 Edition (#2447)

Author: martinmose

uniffi_bindgen/src/scaffolding/templates/Checksums.rs

@@ -1,5 +1,5 @@
 {%- for (name, checksum) in ci.iter_checksums() %}
-#[no_mangle]
+#[unsafe(no_mangle)]
 #[doc(hidden)]
 pub extern "C" fn r#{{ name }}() -> u16 {
     {{ checksum }}

uniffi_bindgen/src/scaffolding/templates/ReexportUniFFIScaffolding.rs

@@ -20,7 +20,7 @@ pub const fn uniffi_reexport_hack() {}
 macro_rules! uniffi_reexport_scaffolding {
     () => {
         #[doc(hidden)]
-        #[no_mangle]
+        #[unsafe(no_mangle)]
         pub extern "C" fn {{ ci.namespace() }}_uniffi_reexport_hack() {
             $crate::uniffi_reexport_hack()
         }

uniffi_bindgen/src/scaffolding/templates/UdlMetadata.rs

@@ -9,5 +9,5 @@ const {{ const_udl_var }}: ::uniffi::MetadataBuffer = ::uniffi::MetadataBuffer::
     .concat_str("{{ udl_base_name }}");
 
 #[doc(hidden)]
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub static {{ static_udl_var }}: [u8; {{ const_udl_var }}.size] = {{ const_udl_var }}.into_array();