create super strict rust config

crates/the-lib/src/lib.rs

@@ -0,0 +1,18 @@
+#[must_use]
+pub const fn add(
+    left: u64,
+    right: u64,
+) -> u64 {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}