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/common/src/mcp_common/microstructure.py

@@ -36,10 +36,7 @@ def orderbook_imbalance(
     ask_vol = sum(q for _, q in top_asks)
     total = bid_vol + ask_vol
 
-    if total == 0:
-        ratio = None
-    else:
-        ratio = (bid_vol - ask_vol) / total
+    ratio = None if total == 0 else (bid_vol - ask_vol) / total
 
     # Microprice: best bid, best ask. Weighted by opposite-side size.
     microprice = None