Some minor restructuring and improvements

common/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "common"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+serde = { version = "1", features = ["derive"] }

common/src/lib.rs

@@ -0,0 +1,4 @@
+#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+pub struct BaseDemoInfo {
+    pub id: i64,
+}