fix: Fix unresolved imports for sha2 and DigestEngine, add Enum macro, remove unused imports

src/digest_engine/none.rs

@@ -1,5 +1,5 @@
 use std::io;
-use log::*;
+use crate::digest_engine::DigestEngine;
 
 #[derive(Debug, Eq, PartialEq, Clone, Default)]
 pub struct DigestEngineNone {}