Remove the cargo.toml workspace and define common as a library

common/src/lib.rs

@@ -0,0 +1,6 @@
+mod recipes {
+    #[test]
+    fn it_works() {
+        assert_eq!(2 + 2, 4);
+    }
+}

common/src/main.rs

@@ -1,3 +0,0 @@
-fn main() {
-    println!("Hello, world!");
-}