refactor(tproxy): migrate to async CloudflareSolver

Replaces synchronous CloudflareSolver with AsyncCloudflareSolver to improve performance and eliminate blocking operations in the proxy addon.

Key improvements:
- Removes httpx dependency in favor of async solver's built-in request handling
- Converts host-level locks from threading.Event to asyncio.Event for proper async coordination
- Implements lazy solver initialization to avoid pre-connection overhead
- Consolidates challenge solving and refetching logic into unified async fetch method
- Adds configurable polling_interval parameter for task result polling
- Extracts clearance cookies directly from solver session state instead of API response parsing

Eliminates ~200 lines of redundant code by leveraging solver's native capabilities for request handling, cookie management, and response processing.

Author: zetxtech