Fix LocalProtocolError

✅ Solution

LocalProtocolError in httpx often arises from modifying data structures (like request headers or the connection pool) while they are being iterated over or used by httpx's internal processes during a request. To resolve this, ensure that you create copies of data structures before modifying them, especially when dealing with request headers or connection pool parameters within middleware or event hooks. Specifically, use `.copy()` on dictionaries or create new lists from deques before iterating and modifying them.