embassy-net: add flush to TcpSocket and TcpWriter as an inherent method

embassy-net/src/tcp.rs

@@ -63,6 +63,10 @@ impl<'a> TcpWriter<'a> {
     pub async fn write(&mut self, buf: &[u8]) -> Result<usize, Error> {
         self.io.write(buf).await
     }
+
+    pub async fn flush(&mut self) -> Result<(), Error> {
+        self.io.flush().await
+    }
 }
 
 impl<'a> TcpSocket<'a> {
@@ -146,6 +150,10 @@ impl<'a> TcpSocket<'a> {
         self.io.write(buf).await
     }
 
+    pub async fn flush(&mut self) -> Result<(), Error> {
+        self.io.flush().await
+    }
+
     pub fn set_timeout(&mut self, duration: Option<Duration>) {
         self.io.with_mut(|s, _| s.set_timeout(duration))
     }