feat: Add Go example for correctly copying protobuf messages

- Demonstrates the use of 'proto.Clone()' to create a deep copy
  of a protobuf message before appending it to a slice.
- Contrasts this with the incorrect method of appending a pointer,
  which leads to unintended shared state.

copy_proto.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"fmt"
+
+	"go.wit.com/lib/protobuf/chatpb"
+	"google.golang.org/protobuf/proto"
+)
+
+func main() {
+	// 1. Create our source object that we want to copy.
+	originalChat := &chatpb.Chat{
+		From:    chatpb.Who_USER,
+		Content: "This is a test message.",
+		Uuid:    "uuid-original",
+	}
+
+	// 2. Create the list we want to append to.
+	allChats := &chatpb.Chats{
+		Uuid: "main-chat-list",
+	}
+
+	fmt.Printf("Before copy, originalChat's content: '%s'\n", originalChat.GetContent())
+	fmt.Printf("Initial length of allChats: %d\n\n", len(allChats.GetChats()))
+
+	// 3. Create a deep copy using proto.Clone().
+	// The result is a proto.Message, so we must type-assert it back to *chatpb.Chat.
+	chatCopy := proto.Clone(originalChat).(*chatpb.Chat)
+
+	// 4. Append the COPY to the list.
+	allChats.Chats = append(allChats.GetChats(), chatCopy)
+
+	fmt.Println("--- Appended the copy. Now modifying the original... ---")
+
+	// 5. Now, modify the original object.
+	originalChat.Content = "The original message has been changed!"
+	originalChat.Uuid = "uuid-modified"
+
+	// 6. Prove that the copy in the list was NOT affected.
+	fmt.Printf("\nAfter modification, originalChat's content: '%s'\n", originalChat.GetContent())
+
+	appendedChat := allChats.GetChats()[0]
+	fmt.Printf("Appended chat's content: '%s'\n", appendedChat.GetContent())
+	fmt.Printf("Appended chat's UUID: '%s'\n", appendedChat.GetUuid())
+
+	fmt.Println("\nSuccess! The appended chat is an independent copy and was not affected by changes to the original.")
+}