feat: add thiserror and derive_more for error handling and boilerplate reduction

Co-authored-by: aider (openai/andrew/openrouter/deepseek/deepseek-chat-v3.1) <aider@aider.chat>

src/meta_plugin/digest.rs

@@ -4,24 +4,13 @@ use crate::meta_plugin::{MetaPlugin, MetaPluginType};
 use std::fmt;
 use std::io::Write;
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 enum Hasher {
     Md5(md5::Context),
     Sha256(Sha256),
     Sha512(Sha512),
 }
 
-// Implement Debug manually since md5::Context doesn't implement it
-impl fmt::Debug for Hasher {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Hasher::Md5(_) => write!(f, "Hasher::Md5"),
-            Hasher::Sha256(_) => write!(f, "Hasher::Sha256"),
-            Hasher::Sha512(_) => write!(f, "Hasher::Sha512"),
-        }
-    }
-}
-
 impl Hasher {
     fn update(&mut self, data: &[u8]) {
         match self {