refactor: 将 DTLS 本地依赖迁移到 libs 目录

libs/dtls/src/handshake/handshake_message_server_hello_done.rs

@@ -0,0 +1,27 @@
+#[cfg(test)]
+mod handshake_message_server_hello_done_test;
+
+use std::io::{Read, Write};
+
+use super::*;
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct HandshakeMessageServerHelloDone;
+
+impl HandshakeMessageServerHelloDone {
+    pub fn handshake_type(&self) -> HandshakeType {
+        HandshakeType::ServerHelloDone
+    }
+
+    pub fn size(&self) -> usize {
+        0
+    }
+
+    pub fn marshal<W: Write>(&self, _writer: &mut W) -> Result<()> {
+        Ok(())
+    }
+
+    pub fn unmarshal<R: Read>(_reader: &mut R) -> Result<Self> {
+        Ok(HandshakeMessageServerHelloDone {})
+    }
+}