fix: Fix unused imports and ProgramWriter issues

src/digest_engine.rs

@@ -1,6 +1,5 @@
-use anyhow::{anyhow, Context, Result};
+use anyhow::{anyhow, Result};
 use std::io;
-use std::io::{Read, Write};
 
 use log::*;
 
@@ -37,23 +36,9 @@ pub trait DigestEngine {
     fn update(&mut self, data: &[u8]);
 }
 
-// Dummy writer that implements Write for the none digest engine
-struct DummyWriter;
-
-impl DummyWriter {
-    fn new() -> Self {
-        DummyWriter
-    }
-}
-
-impl Write for DummyWriter {
-    fn write(&mut self, _buf: &[u8]) -> io::Result<usize> {
-        Ok(0)
-    }
-
-    fn flush(&mut self) -> io::Result<()> {
-        Ok(())
-    }
+// Writer that implements Write for the program digest engine
+struct ProgramWriter {
+    stdin: std::process::ChildStdin,
 }
 
 lazy_static! {