Add comprehensive test coverage for HTTP/SSE server and docs tools

- HTTP/SSE server: Add tests for app initialization and session management
- Docs tools: Add tests for cache functionality, error handling, and network errors
- Make components more testable by exposing necessary fields
- Add mockito for HTTP testing support
- Improve robust error handling in network tests
- Add Tower util feature for ServiceExt support

src/tools/docs/docs.rs

@@ -43,8 +43,8 @@ impl DocCache {
 
 #[derive(Clone)]
 pub struct DocRouter {
-    client: Client,
-    cache: DocCache,
+    pub client: Client,
+    pub cache: DocCache,
 }
 
 impl Default for DocRouter {