Write `get-file` and commands to get the list of blocks from another node

Description

This closes #1 (closed) by providing an API that allows to get a file with just its hash

Detailed list of changes

• add get_file, get_blocks_info_from and other things related to managing the filesystem
• add new commands to nu API
• remove DragoonBehaviour as it was not useful
• add two new tests for get_file and change the already existing test to use the new API

Note

The get_file is still very rough, the error management needs to be handled better to take into a lot more cases of failure

src/commands.rs

@@ -117,7 +117,7 @@ pub(crate) enum DragoonCommand {
         file_hash: String,
         output_filename: String,
         powers_path: String,
-        sender: Sender<String>,
+        sender: Sender<PathBuf>,
     },
     GetFileDir {
         file_hash: String,
@@ -417,7 +417,9 @@ pub(crate) async fn create_cmd_start_provide(
 // End of dragoon command implementation
 
 fn handle_dragoon_error(err: Box<dyn Error + Send>, command: &str) -> Response {
-    format!("Got error from command `{}`: {}", command, err).into_response()
+    let err_msg = format!("Got error from command `{}`: {}", command, err);
+    error!(err_msg);
+    DragoonError::UnexpectedError(err_msg).into_response()
 }
 
 fn handle_canceled(err: RecvError, command: &str) -> Response {