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/templates/smb/server.py

@@ -22,6 +22,7 @@ from __future__ import annotations
 import asyncio
 import os
 import struct
+from typing import cast
 
 import instance_seed
 from ntlmssp import find_ntlmssp, parse_type3
@@ -184,7 +185,7 @@ def _negotiate_response(message_id: int) -> bytes:
         + struct.pack("<H", 0)              # SecurityBufferLength
         + struct.pack("<I", 0)              # Reserved2
     )
-    return _smb2_header(SMB2_NEGOTIATE, STATUS_SUCCESS, message_id) + body
+    return cast(bytes, _smb2_header(SMB2_NEGOTIATE, STATUS_SUCCESS, message_id) + body)
 
 
 def _session_setup_response(message_id: int, session_id: int, sec_blob: bytes, status: int) -> bytes: