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.

pyproject.toml

@@ -15,7 +15,7 @@ target-version = "py313"
 
 [tool.ruff.lint]
 select = ["E", "F", "I", "W", "UP", "B", "SIM"]
-ignore = ["E501"]
+ignore = ["E501", "E741"]
 
 [tool.ruff.lint.flake8-bugbear]
 extend-immutable-calls = [