feat: list systemd services in one round trip and control them, once for every driver

Listing a host's services and starting or stopping one is the same on every
host that runs systemd, so the command, its parse, the check of a unit name
and the reading of an action's exit status live here once, and a driver
supplies only the transport (napalm-linux#7, napalm-proxmox#6):

- SYSTEMD_SERVICES_COMMAND: one read-only POSIX sh line. list-unit-files, then
  one systemctl show over every loaded service unit (Id, Names, LoadState,
  ActiveState, SubState, UnitFileState, MainPID), and is-enabled only for
  generated units, whose boot state lives in a SysV script's rc links. Framed;
  [no-systemd] when /run/systemd/system is missing. Replaces an is-enabled and
  a show per unit: 0.8 s instead of 6 s on a 180-unit Ubuntu host.
- parse_systemd_services(): loaded units except not-found, plus installed unit
  files that are not loaded; no templates, no aliases (also not the ones older
  systemd lists as "enabled"). enabled = UnitFileState enabled or
  enabled-runtime, read from systemctl show and never from list-unit-files'
  second column, which has had a preset column after it since systemd 245.
  A report whose end is missing raises ValueError, so a list cut short never
  reads as services that went away; a host without systemd raises
  SystemdUnavailable, a NotImplementedError, so a driver can fall back.
- unit_name() / service_action_command() / parse_action_result(): template
  instances, dots, colons and \xHH escapes accepted; a bare template, a leading
  "-" and anything a shell reads refused. The action runs as
  "timeout 45 systemctl --no-ask-password <action> -- <unit>.service" with its
  exit status printed after it; only that status decides, 124 is not called
  done, and terminal colour codes are dropped. The marker also keeps the output
  from ever being empty, which a transport that retries on an empty answer
  would take as a reason to run the action twice.
- SystemdServicesMixin, in the template form: get_services() and
  manage_service() are concrete, _run_service_command(command, *, privileged,
  timeout) is the driver's hook. Mixed in by the drivers whose host runs
  systemd, not by OSDriver.

Version 2.2.0.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "napalm-device-types"
-version = "2.1.0"
+version = "2.2.0"
 description = "Abstract device-type base classes for NAPALM drivers"
 readme = "README.md"
 requires-python = ">=3.10"