clippy: Allow unused imports

We can remove this once `pasta_curves` has been updated to remove
`CurveAffine::read`.

src/lib.rs

@@ -21,6 +21,8 @@
 #![deny(missing_debug_implementations)]
 #![deny(missing_docs)]
 #![deny(unsafe_code)]
+// Remove this once we update pasta_curves
+#![allow(unused_imports)]
 
 pub mod arithmetic;
 pub mod circuit;