vyos: T9261: defer more heavy imports off the CLI hot paths

Follow-up sweep to f696b2d65. Every conf-mode script not handled in-daemon by
vyos-configd, every op-mode script and every Python validator is a fresh
interpreter, so module-scope imports of heavy dependencies are paid over and
over - which is what makes the CLI feel sluggish on CPUs with little cache.

configsource.py imported vyos.vyconf_session, and with it google.protobuf, for
a class that is only instantiated when the vyconf backend is active. opmode.py
imported ConfigTreeQuery for a single decorator most op-mode scripts never use.
template.py imported jinja2 at module scope although Environment is only touched
in the lru_cache'd _get_environment(), while most callers want just the
is_ipv4/is_ipv6 predicates. ethtool.py pulled pyroute2 via vyos.netlink for two
calls in Ethtool.__init__. ifconfig/interface.py pulled the whole cryptography
stack via vyos.pki for set_eapol() alone. Also deferred: netaddr, jmespath,
tabulate, hurry.filesize, vyos.ifconfig in qos, and cracklib - the last of which
also opens its dictionary database on import.

  import vyos.opmode      34.0 -> 4.6 ms   (-86%), 206 -> 71 modules
  import vyos.ifconfig   132.9 -> 30.8 ms  (-77%), 618 -> 193 modules
  import vyos.config      40.7 -> 20.6 ms  (-49%), 194 -> 130 modules
  import vyos.qos        134.1 -> 12.5 ms  (-91%), 631 -> 124 modules
  import vyos.template    18.8 -> 6.3 ms   (-66%), 153 -> 89 modules
  import vyos.firewall    22.2 -> 12.2 ms  (-45%), 168 -> 114 modules

Deferring textwrap in base.py and logging in configtree.py was measured too and
made no difference; both were left alone.

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