sync api with refsol

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-starter/src/lsm_storage.rs

@@ -158,6 +158,10 @@ impl MiniLsm {
         self.inner.delete(key)
     }
 
+    pub fn sync(&self) -> Result<()> {
+        self.inner.sync()
+    }
+
     pub fn scan(
         &self,
         lower: Bound<&[u8]>,
@@ -222,6 +226,10 @@ impl LsmStorageInner {
         Ok(storage)
     }
 
+    pub fn sync(&self) -> Result<()> {
+        unimplemented!()
+    }
+
     /// Get a key from the storage. In day 7, this can be further optimized by using a bloom filter.
     pub fn get(&self, _key: &[u8]) -> Result<Option<Bytes>> {
         unimplemented!()