Remove unused code and modernize Rust format strings

Applied cargo clippy fixes to clean up codebase:
- Removed unused imports (serde_json::json, std::collections::HashSet)
- Removed unused function encode_hex_for_log
- Modernized format strings to use inline variables
- Fixed clippy warnings for better code quality

All changes applied automatically by cargo clippy --fix

src-tauri/src/extension/error.rs

@@ -174,7 +174,7 @@ impl serde::Serialize for ExtensionError {
         let mut state = serializer.serialize_struct("ExtensionError", 4)?;
 
         state.serialize_field("code", &self.code())?;
-        state.serialize_field("type", &format!("{:?}", self))?;
+        state.serialize_field("type", &format!("{self:?}"))?;
         state.serialize_field("message", &self.to_string())?;
 
         if let Some(ext_id) = self.extension_id() {