chore(types): enable warn_return_any and cast all no-any-return sites

Turn on mypy warn_return_any (pyproject) and resolve the 84 resulting
[no-any-return] errors across 43 files with typing.cast() at the return
sites — runtime no-ops that make the declared return type explicit where a
dependency (SQLAlchemy scalar/first/one, httpx .json(), subprocess, docker
SDK) hands back Any. No behavior change: no DTO/table field types altered, no
validation/coercion calls added, every cast reflects the true runtime type.

Locks in return-type strictness so the class of bug where a function silently
widens to Any can't regress. mypy decnet/ clean; adversarially verified
behavior-preserving (84 casts 1:1 with prior returns).

Bump tornado 6.5.5 -> 6.5.7 (CVE-2026-49854, transitive via snakeviz).

decnet/ttp/misp_export.py

@@ -16,7 +16,7 @@ build_fleet_misp_collection → dict  ({"response": [event, ...]})
 from __future__ import annotations
 
 import json
-from typing import Any
+from typing import Any, cast
 
 from misp_stix_converter import ExternalSTIX2toMISPParser
 
@@ -35,7 +35,7 @@ def _parse_bundle(bundle: Any) -> dict[str, Any]:
     event = parser.misp_events
     if event is None:
         return {}
-    return json.loads(event.to_json())
+    return cast(dict[str, Any], json.loads(event.to_json()))
 
 
 def build_attacker_misp_event(