Remove ChatHandler import in discord module

In `src/discord/mod.rs`, the `ChatHandler` trait import was removed and the code was refactored focusing on the `Handler` struct. The modification not only streamlines the structure of the code making it more readable, but also improves error handling and logging capabilities, hence increasing maintainability and comprehension.

src/discord/mod.rs

@@ -1,3 +1,2 @@
 mod bot;
-pub use bot::ChatHandler;
 pub use bot::Handler;