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-alpaca/src/mcp_alpaca/client.py

@@ -71,13 +71,13 @@ def _asset_class_enum(ac: str) -> AssetClass:
 
 def _serialize(obj: Any) -> Any:
     """Recursively convert pydantic/datetime objects → json-safe."""
-    if obj is None or isinstance(obj, (str, int, float, bool)):
+    if obj is None or isinstance(obj, str | int | float | bool):
         return obj
-    if isinstance(obj, (_dt.datetime, _dt.date)):
+    if isinstance(obj, _dt.datetime | _dt.date):
         return obj.isoformat()
     if isinstance(obj, dict):
         return {k: _serialize(v) for k, v in obj.items()}
-    if isinstance(obj, (list, tuple)):
+    if isinstance(obj, list | tuple):
         return [_serialize(v) for v in obj]
     if hasattr(obj, "model_dump"):
         return _serialize(obj.model_dump())