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/hbdclass.py

@@ -8,6 +8,7 @@ import time
 import json
 import copy
 import queue
+from typing import Any, Dict
 
 num = 0
 
@@ -24,7 +25,7 @@ def log(host, m):
 class Connection:
     # map of addrs to names
 
-    htab = {}
+    htab: Dict[str, Any] = {}
     UNKNOWN = "unknown"
     UP = "up"
     DOWN = "down"
@@ -278,8 +279,8 @@ class Connection:
 #
 class Host:
     # Table of Hosts
-    hosts = {}
-    dnsQ = queue.Queue()
+    hosts: Dict[str, "Host"] = {}
+    dnsQ: "queue.Queue[Any]" = queue.Queue()
 
     def __init__(self, name):
         global num