refactor storage layer

src-tauri/migrations/20230814083543_add_events_table.sql

@@ -0,0 +1,9 @@
+-- Add migration script here
+CREATE TABLE
+  events (
+    id INTEGER NOT NULL PRIMARY KEY,
+    cache_key TEXT NOT NULL UNIQUE,
+    event_id TEXT NOT NULL UNIQUE,
+    event_kind INTEGER NOT NULL DEFAULT 1,
+    event TEXT NOT NULL
+  );