feat!: settle the open review questions; release 4.7.0

## feat!: settle the open review questions on roles, diffs, SSH and SNMP

- roles: a driver that sets ROLE itself replaces the role it inherits,
  so a Windows driver on OSDriver is "windows", not also "linux".
- os: OSDriver's account listing is get_os_users; NAPALM's get_users has
  another shape and a runtime stub, so hasattr could not tell.
- README: NAPALM's own getters must come from the driver or a mixin
  listed before the first role base; its stubs win the MRO otherwise.
- firewall/DHCP diffs: an empty key, a key given twice, or one more than
  one live entry holds raises ValueError instead of overwriting by guess;
  live entries without a key are never matched.
- ssh_server: only host key algorithms the host has a key for count as
  staying; when the keys cannot be read, the host key list is not
  touched. sshd_config and its copy keep their file mode (GNU and BSD
  stat), 644 only for a new file.
- SNMP: 64-bit ifXTable octets and ifHighSpeed, with the 32-bit counters
  as fallback for agents without ifXTable.
- pyproject: declare typing-extensions, which models.py imports.

BREAKING CHANGE: OSDriver.get_users is now get_os_users; diffs raise
ValueError on keys that cannot name one entry; plan_ssh_hardening
removes no host key algorithm without host_keys.

## fix: tell "could not read" and "does not install" apart in update and VIP readers

- package_updates: the dnf security reader records dnf's exit status and
  raises when it is missing or non-zero, as the apt reader does; a failed
  dnf no longer reads as "no security advisories".
- host_status: an enabled dnf-automatic.timer counts as auto updates only
  with apply_updates = yes (dnf5's automatic.conf wins over dnf4's);
  dnf-automatic-install.timer always does. Unattended-upgrades counts only
  while the program is installed, not from a conffile left behind.
- virtual_ips: a host with systemctl but without systemd as PID 1 reads as
  "did not look" (None), not as "has none". keepalived blocks whose brace
  is on the next line are read.

BREAKING CHANGE: parse_dnf_security expects DNF_SECURITY_COMMAND's
__DNF_RC marker and raises ValueError without it.

README.md

@@ -74,6 +74,14 @@ Two things follow, and both are improvements:
 - **A method that was never implemented raises `AttributeError`, not
   `NotImplementedError`.** Ask before calling.
 
+The rule covers this package's methods, not NAPALM's. `NetworkDriver` still carries
+a runtime `NotImplementedError` stub for each of its getters (`get_interfaces`,
+`get_environment`, `get_users`, …), and every role base inherits it. So a NAPALM getter
+must come from the driver class itself or from a mixin listed **before** the first role
+base; a mixin listed after it loses the MRO to NAPALM's stub. For the same reason
+`hasattr` says nothing about NAPALM's getters, and the OS role's account listing is
+`get_os_users`, not `get_users` -- NAPALM's `get_users` has a different shape.
+
 ## Function classes: what a device *can do*
 
 Behaviour shared across roles lives in a function class, exactly once, and a role base
@@ -378,8 +386,8 @@ class LinuxDriver(OSDriver):
         # return List[ServiceDict]
         ...
 
-    def get_users(self):
-        # return List[UserDict]
+    def get_os_users(self):
+        # return List[UserDict] -- not NAPALM's get_users, whose shape differs
         ...
 
     def get_processes(self):