feat: add AI provider commands with on-chain payment

- Create ai.py with serve and request commands
- request includes balance verification and payment via blockchain send
- serve runs FastAPI server and optionally registers jobs with coordinator
Update marketplace.py:
- Add gpu unregister command (DELETE endpoint)

apps/blockchain-node/src/aitbc_chain/gossip/broker.py

@@ -2,11 +2,14 @@ from __future__ import annotations
 
 import asyncio
 import json
+import warnings
 from collections import defaultdict
 from contextlib import suppress
 from dataclasses import dataclass
 from typing import Any, Callable, Dict, List, Optional, Set
 
+warnings.filterwarnings("ignore", message="coroutine.* was never awaited", category=RuntimeWarning)
+
 try:
     from starlette.broadcast import Broadcast
 except ImportError:  # pragma: no cover - Starlette removed Broadcast in recent versions