additional fields encoding and decoding

src/data/entities.rs

@@ -1,5 +1,5 @@
 use crate::core::srs::{FADE_PER_DAY, MAX_SCORE, WordOpenMode};
-use crate::data::{INVALID_ID, Id};
+use crate::data::{Id, SmallId, INVALID_ID};
 use crate::data_provider::history::HistoryRepositoryInner;
 use chrono::{DateTime, Local, NaiveDate, Utc};
 use fsrs::MemoryState;
@@ -19,7 +19,7 @@ pub struct WordData {
     pub key: String,
     pub value: String,
     pub tags: String,
-    pub additional: LiteMap<String, String>,
+    pub additional: LiteMap<Id, String>,
 }
 
 impl EntityData for WordData {