add wal and manifest

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

mini-lsm/src/compact/leveled.rs

@@ -1,7 +1,10 @@
 use std::collections::HashSet;
 
+use serde::{Deserialize, Serialize};
+
 use crate::lsm_storage::LsmStorageState;
 
+#[derive(Serialize, Deserialize)]
 pub struct LeveledCompactionTask {
     // if upper_level is `None`, then it is L0 compaction
     pub upper_level: Option<usize>,