Enforce important cast-related lints.

src/lib.rs

@@ -208,6 +208,14 @@
 #![no_std]
 #![warn(rust_2018_idioms, unused_lifetimes, missing_docs)]
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![deny(
+    clippy::unnecessary_cast,
+    clippy::cast_lossless,
+    clippy::cast_possible_truncation,
+    clippy::cast_possible_wrap,
+    clippy::cast_precision_loss,
+    clippy::cast_sign_loss
+)]
 
 #[macro_use]
 extern crate cfg_if;