export_service! macro should correctly name records wrapped in `ManualReply`s

Reproduce the issue with the Rust example using candid::export_service! and run cargo test to inspect the generated test.did file. Start by tracing how export_service! handles ManualReply return types; done means the generated candid names the wrapped record User rather than ManualReply or an incremented variant.

Describe the bug
The candid export service doesn't correctly handle canister methods with a return type of ManualReply. Instead of exporting the record type in the canister method signature, it exports a generic ManualReply type. Subsequent ManualReplys will be given incrementing names of format ManualReply_n where n increases for the amount of records.

To Reproduce
Steps to reproduce the behavior:

1. Create a Rust canister with the following contents:

   use ic_cdk::api::call::{self, ManualReply};
   
   #[derive(candid::CandidType)]
   struct User {
       id: String,
   }
   
   #[ic_cdk_macros::query]
   #[candid::candid_method(query)]
   async fn method() -> ManualReply<User> {
       let user = User {
           id: "a".to_string(),
       };
       call::reply((user,));
       ManualReply::empty()
   }
   
   candid::export_service!();
   #[ic_cdk_macros::query(name = "__get_candid_interface_tmp_hack")]
   fn export_candid() -> String {
       __export_service()
   }
   
   #[cfg(test)]
   mod tests {
       use super::*;
       #[test]
       fn write_candid_to_disk() {
           std::fs::write("test.did", export_candid()).unwrap();
       }
   }
   

   Full example can be found at https://github.com/dansteren/candid_export_bug

2. Run cargo test

3. Inspect the generated candid file at canisters/tests/test.did

4. Notice that it contains a type ManualReply which doesn't have the same name as the User struct in canisters/test/src/lib.rs

   type ManualReply = record { id : text };
   service : { method : () -> (ManualReply) query }
   

Expected behavior
The candid file should name the user type User not ManualReply. I.e.

type User = record { id : text };
service : { method : () -> (User) query }

Screenshots
N/A

Platform

• OS: Ubuntu 22.04
• Rust Version: rustc 1.63.0 (4b91a6ea7 2022-08-08)
• DFX Version: 0.11.0
• Candid Crate Version: 0.7.4

Additional context
The problem occurs regardless of whether the function is a Query or an Update. The problem does not occur if another function also returns that type (See https://github.com/dansteren/candid_export_bug/tree/include_type_in_other_function_sig).

PS: Your Bug issue template isn't working so I was unable to apply the Bug label.