lint: ruff clean services/ (autofix + manual + ignore E741)

- 24 autofix safe (SIM105 contextlib.suppress, F401 unused imports,
  I001 import order, B007 unused loop var, F811 redef, F841 unused).
- 15 unsafe-fix (UP038 X|Y in isinstance, SIM108 ternary, ecc.).
- Manual fix: SIM102 nested if in deribit term_structure, E402 imports
  in test_cot.py + sentiment server.py.
- Ignore E741 (variabili 'l' in list comprehensions deribit/client.py
  — stilistico, non bug).

Tests: 478/478 verdi.

services/mcp-hyperliquid/src/mcp_hyperliquid/client.py

@@ -6,7 +6,6 @@ import asyncio
 import datetime as _dt
 from typing import Any
 
-import httpx
 from mcp_common import indicators as ind
 from mcp_common.http import async_client