Preserve symlinks in file copy

tests/integration_smoke.rs

@@ -1003,6 +1003,8 @@ fn native_file_copy_recursive_round_trip() {
     fs::create_dir_all(src.join("nested")).unwrap();
     fs::write(src.join("root.txt"), b"root file\n").unwrap();
     fs::write(src.join("nested/child.txt"), b"child file\n").unwrap();
+    std::os::unix::fs::symlink("root.txt", src.join("root-link")).unwrap();
+    std::os::unix::fs::symlink("nested/child.txt", src.join("child-link")).unwrap();
 
     let client_bin = env!("CARGO_BIN_EXE_dosh-client");
     let upload = Command::new(client_bin)
@@ -1108,6 +1110,14 @@ fn native_file_copy_recursive_round_trip() {
         fs::read_to_string(downloaded.join("nested/child.txt")).unwrap(),
         "child file\n"
     );
+    assert_eq!(
+        fs::read_link(downloaded.join("root-link")).unwrap(),
+        PathBuf::from("root.txt")
+    );
+    assert_eq!(
+        fs::read_link(downloaded.join("child-link")).unwrap(),
+        PathBuf::from("nested/child.txt")
+    );
 
     let remove = Command::new(client_bin)
         .arg("--dosh-host")