feat(core/database): implement File operations

crates/core/database/src/drivers/reference.rs

@@ -2,7 +2,7 @@ use std::{collections::HashMap, sync::Arc};
 
 use futures::lock::Mutex;
 
-use crate::{Bot, User};
+use crate::{Bot, File, User};
 
 database_derived!(
     /// Reference implementation
@@ -10,5 +10,6 @@ database_derived!(
     pub struct ReferenceDb {
         pub bots: Arc<Mutex<HashMap<String, Bot>>>,
         pub users: Arc<Mutex<HashMap<String, User>>>,
+        pub files: Arc<Mutex<HashMap<String, File>>>,
     }
 );