Enforce stricter lints

Copied from Attic.

gha-cache/src/lib.rs

@@ -1,4 +1,17 @@
-//! Meow.
+#![deny(
+    asm_sub_register,
+    deprecated,
+    missing_abi,
+    unsafe_code,
+    unused_macros,
+    unused_must_use,
+    unused_unsafe
+)]
+#![deny(clippy::from_over_into, clippy::needless_question_mark)]
+#![cfg_attr(
+    not(debug_assertions),
+    deny(unused_imports, unused_mut, unused_variables,)
+)]
 
 pub mod api;
 pub mod credentials;

nix-actions-cache/src/main.rs

@@ -1,3 +1,18 @@
+#![deny(
+    asm_sub_register,
+    deprecated,
+    missing_abi,
+    unsafe_code,
+    unused_macros,
+    unused_must_use,
+    unused_unsafe
+)]
+#![deny(clippy::from_over_into, clippy::needless_question_mark)]
+#![cfg_attr(
+    not(debug_assertions),
+    deny(unused_imports, unused_mut, unused_variables,)
+)]
+
 mod error;
 
 use std::io;