Fix: Remove serde feature detection from declare_raft_types! macro

The `[cfg_attr(feature = "serde")]` feature detection for
`RaftTypeConfig` implementation should not be evaluated in application
crates when the `declare_raft_types!` macro is called. This detection
logic should be removed from the macro and instead added to each type
that uses `RaftTypeConfig`.

Author: drmingdrmer

openraft/src/raft/declare_raft_types_test.rs

@@ -1,5 +1,7 @@
 //! Test the `declare_raft_types` macro with default values
 
+#![allow(dead_code)]
+
 use std::io::Cursor;
 
 use crate::declare_raft_types;

openraft/src/raft/mod.rs

@@ -152,7 +152,6 @@ macro_rules! declare_raft_types {
     ($(#[$outer:meta])* $visibility:vis $id:ident: $($(#[$inner:meta])* $type_id:ident = $type:ty),* $(,)? ) => {
         $(#[$outer])*
         #[derive(Debug, Clone, Copy, Default, Eq, PartialEq, Ord, PartialOrd)]
-        #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
         $visibility struct $id {}
 
         impl $crate::RaftTypeConfig for $id {