feat: add serde derive to Score types

This commit adds `serde` dependency and derives `Serialize` trait for `Score` types. This is necessary for serialization and deserialization of these types, which is required to display Scores to various user interfaces

- Added `serde` dependency to `harmony_types/Cargo.toml`.
- Added `serde::Serialize` derive macro to `MacAddress` in `harmony_types/src/lib.rs`.
- Added `serde::Serialize` derive macro to `Config` in `opnsense-config/src/config/config.rs`.
- Added `serde::Serialize` derive macro to `Score` in `harmony_types/src/lib.rs`.
- Added `serde::Serialize` derive macro to `Config` and `Score` in relevant modules.
- Added placeholder `todo!()` implementations for `serialize` methods. These will be implemented in future commits.

harmony_types/src/lib.rs

@@ -1,5 +1,7 @@
 pub mod net {
-    #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+    use serde::Serialize;
+
+    #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, Serialize)]
     pub struct MacAddress(pub [u8; 6]);
 
     impl MacAddress {