fix: remove unused digest field from Settings struct

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

src/config.rs

@@ -89,7 +89,6 @@ pub struct Settings {
     pub server: Option<ServerConfig>,
     pub compression_plugin: Option<CompressionPluginConfig>,
     pub meta_plugins: Option<Vec<MetaPluginConfig>>,
-    pub digest: Option<String>,
 }
 
 impl Settings {

src/meta_plugin/digest.rs

@@ -26,7 +26,7 @@ impl Hasher {
     fn update(&mut self, data: &[u8]) {
         match self {
             Hasher::Md5(hasher) => {
-                hasher.write(data);
+                let _ = hasher.write(data);
             },
             Hasher::Sha256(hasher) => hasher.update(data),
             Hasher::Sha512(hasher) => hasher.update(data),

src/meta_plugin/hostname.rs

@@ -81,7 +81,7 @@ impl HostnameMetaPlugin {
             
             // If no reverse lookup worked, but we have addresses, try to construct FQDN
             // from the first address's domain if the short hostname is part of a domain
-            if let Some(first_addr) = addrs.first() {
+            if let Some(_first_addr) = addrs.first() {
                 // For local addresses, we might not get a reverse lookup, so try to infer
                 // from the system's domain name
                 if let Ok(domain) = std::process::Command::new("domainname").output() {

src/modes/common.rs

@@ -169,10 +169,6 @@ pub fn settings_meta_plugin_types(cmd: &mut Command, settings: &config::Settings
     meta_plugin_types
 }
 
-pub fn settings_digest_type(_cmd: &mut Command, _settings: &config::Settings) -> MetaPluginType {
-    // The digest plugin is now unified, always return Digest
-    MetaPluginType::Digest
-}
 
 pub fn settings_compression_type(cmd: &mut Command, settings: &config::Settings) -> CompressionType {
     let compression_name = settings