fix: commit txn when dropping

it's less confusing

crates/loro-internal/src/loro.rs

@@ -52,11 +52,18 @@ pub struct LoroDoc {
     arena: SharedArena,
     observer: Arc<Observer>,
     diff_calculator: Arc<Mutex<DiffCalculator>>,
+    // when dropping the doc, the txn will be commited
     txn: Arc<Mutex<Option<Transaction>>>,
     auto_commit: bool,
     detached: bool,
 }
 
+impl Default for LoroDoc {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl LoroDoc {
     pub fn new() -> Self {
         let oplog = OpLog::new();
@@ -664,18 +671,6 @@ fn parse_encode_header(bytes: &[u8]) -> Result<(&[u8], EncodeMode), LoroError> {
     Ok((&input[1..], mode))
 }
 
-impl Default for LoroDoc {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
-impl Drop for LoroDoc {
-    fn drop(&mut self) {
-        self.abort_txn();
-    }
-}
-
 #[cfg(test)]
 mod test {
     use loro_common::ID;