stubbed some methods for db interaction

src/db/mod.rs

@@ -1,4 +1,4 @@
-use std::fmt;
+use std::{fmt, path::PathBuf};
 
 use {
     crate::{Package, Repository, Version},
@@ -91,4 +91,16 @@ impl Database {
         }
         Ok(updates)
     }
+
+    pub fn from_file(prefix: Option<PathBuf>) -> Result<File, Box<dyne Error>> {
+        unimplemented!();
+    }
+
+    pub fn save_to_file(prefix: Option<PathBuf>) -> Result<(), Box<dyn Error>> {
+        unimplemented!();
+    }
+
+    pub fn rebuild(prefix: Option<PathBuf>) -> Result<(), Box<dyn Error>> {
+        unimplemented!();
+    }
 }