Fix nightly clippy warnings (#925)

* Derive `Default`

* Fix `field is never read`

crates/env/src/engine/on_chain/ext.rs

@@ -99,7 +99,7 @@ where
     /// The internal Wasm32 raw pointer value.
     ///
     /// Must not be readable or directly usable by any safe Rust code.
-    value: u32,
+    _value: u32,
     /// We handle types like these as if the associated lifetime was exclusive.
     marker: PhantomData<fn() -> &'a T>,
 }
@@ -111,7 +111,7 @@ where
     /// Creates a new Wasm32 pointer for the given raw pointer value.
     fn new(value: u32) -> Self {
         Self {
-            value,
+            _value: value,
             marker: Default::default(),
         }
     }
@@ -142,7 +142,7 @@ where
     /// The internal Wasm32 raw pointer value.
     ///
     /// Must not be readable or directly usable by any safe Rust code.
-    value: u32,
+    _value: u32,
     /// We handle types like these as if the associated lifetime was exclusive.
     marker: PhantomData<fn() -> &'a mut T>,
 }
@@ -154,7 +154,7 @@ where
     /// Creates a new Wasm32 pointer for the given raw pointer value.
     fn new(value: u32) -> Self {
         Self {
-            value,
+            _value: value,
             marker: Default::default(),
         }
     }

crates/storage/src/collections/bitvec/bits256.rs

@@ -21,20 +21,12 @@ use super::{
 };
 
 /// A chunk of 256 bits.
-#[derive(Debug, Copy, Clone, PartialEq, Eq, scale::Encode, scale::Decode)]
+#[derive(Debug, Copy, Clone, Default, PartialEq, Eq, scale::Encode, scale::Decode)]
 #[cfg_attr(feature = "std", derive(scale_info::TypeInfo))]
 pub struct Bits256 {
     bits: [Bits64; 4],
 }
 
-impl Default for Bits256 {
-    fn default() -> Self {
-        Self {
-            bits: Default::default(),
-        }
-    }
-}
-
 /// Iterator over the valid bits of a pack of 256 bits.
 #[derive(Debug, Copy, Clone)]
 pub struct Iter<'a> {