fix: clear all mypy errors

Annotate untyped containers and Optional attributes, type the stdlib-shaped
metric dicts in the client plugins, and add types-PyYAML/types-psutil to the
dev extras plus a mypy override for nio/mattermostdriver (no stubs).

Behaviour fixes found on the way: enable_kernel_timestamps() now returns False
when SO_TIMESTAMP is unknown instead of raising TypeError, send_shutdown is
defined at module level so cleanup() cannot hit a NameError, and a failed
subprocess returncode falls back to UNKNOWN.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

hbd/server/journal.py

@@ -11,7 +11,7 @@ import os
 import asyncio
 from datetime import datetime
 from pathlib import Path
-from typing import Dict, Any, Optional, Callable, Iterable, List, Tuple, Union
+from typing import Dict, Any, Optional, Callable, Iterable, List, TextIO, Tuple, Union
 
 logger = logging.getLogger(__name__)
 
@@ -52,7 +52,7 @@ class MessageJournal:
         self.enabled = self.config.get('journal_enabled', True)
 
         # Runtime state
-        self._file_handle = None
+        self._file_handle: Optional[TextIO] = None
         self._current_size = 0
         self._lock = asyncio.Lock()
         self._initialized = False