refactor: work on auth chain and state compressor

src/service/rooms/state_compressor/data.rs

@@ -0,0 +1,10 @@
+struct StateDiff {
+    parent: Option<u64>,
+    added: Vec<CompressedStateEvent>,
+    removed: Vec<CompressedStateEvent>,
+}
+
+pub trait Data {
+    fn get_statediff(shortstatehash: u64) -> Result<StateDiff>;
+    fn save_statediff(shortstatehash: u64, diff: StateDiff) -> Result<()>;
+}