Fix critical compilation error in dashcore-rpc

- Move #[allow(unused)] to correct position with crate attributes
- Add missing '!' to make it a proper crate-level attribute
- Resolves clippy compilation failure when warnings are treated as errors

Author: PastaPastaPasta

rpc-client/src/lib.rs

@@ -15,10 +15,10 @@
 
 #![crate_name = "dashcore_rpc"]
 #![crate_type = "rlib"]
+#![allow(unused)]
 
 #[macro_use]
 extern crate log;
-#[allow(unused)]
 #[macro_use] // `macro_use` is needed for v1.24.0 compilation.
 extern crate serde;
 extern crate serde_json;