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/dragoon_network.rs

@@ -1054,7 +1054,7 @@ where
 
     async fn decode_blocks(
         block_dir: PathBuf,
-        block_hashes: &Vec<String>,
+        block_hashes: &[String],
         output_filename: String,
     ) -> Result<()> {
         let blocks =