More accurate "GatewayHello::default()" (#534)

Replaces the derived `std::default::Default` with

```rs
impl std::default::Default for GatewayHello {
    fn default() -> Self {
        Self {
            // "HELLO" opcode is 10
            op: 10,
            d: Default::default(),
        }
    }
}

impl std::default::Default for HelloData {
    fn default() -> Self {
        Self {
            // Discord docs mention 45000 seconds - discord.sex mentions 41250. Defaulting to 45s
            heartbeat_interval: 45000,
        }
    }
}
```

src/types/events/hello.rs

@@ -7,16 +7,38 @@ use chorus_macros::WebSocketEvent;
 use serde::{Deserialize, Serialize};
 
 /// Received on gateway init, tells the client how often to send heartbeats;
-#[derive(Debug, Default, Deserialize, Serialize, Clone, PartialEq, Eq, WebSocketEvent, Copy, Hash, PartialOrd, Ord)]
+#[derive(
+    Debug, Deserialize, Serialize, Clone, PartialEq, Eq, WebSocketEvent, Copy, Hash, PartialOrd, Ord,
+)]
 pub struct GatewayHello {
     pub op: i32,
     pub d: HelloData,
 }
 
-#[derive(Debug, Default, Deserialize, Serialize, Clone, PartialEq, Eq, Copy, WebSocketEvent, Hash, PartialOrd, Ord)]
+#[derive(
+    Debug, Deserialize, Serialize, Clone, PartialEq, Eq, Copy, WebSocketEvent, Hash, PartialOrd, Ord,
+)]
 /// Contains info on how often the client should send heartbeats to the server;
 pub struct HelloData {
     /// How often a client should send heartbeats, in milliseconds
     pub heartbeat_interval: u64,
 }
 
+impl std::default::Default for GatewayHello {
+    fn default() -> Self {
+        Self {
+            // "HELLO" opcode is 10
+            op: 10,
+            d: Default::default(),
+        }
+    }
+}
+
+impl std::default::Default for HelloData {
+    fn default() -> Self {
+        Self {
+            // Discord docs mention 45000 seconds - discord.sex mentions 41250. Defaulting to 45s
+            heartbeat_interval: 45000,
+        }
+    }
+}