feat: packages, services and updates

The write side NetOrk/netork#799 needs, on both drivers.

- Packages: get_packages (FreeBSD `pkg query` with the repository as
  source, nothing on a classic system without pkg; OpenBSD `pkg_info`),
  install_package / uninstall_package as root (`pkg install`/`pkg
  delete`, `pkg_add -I`/`pkg_delete`), names checked before anything is
  sent, a failure raised with what the tool printed.
- Updates: get_available_updates. FreeBSD `pkg upgrade -n`, with
  `security` from VuXML (`pkg audit`: True for a listed package, False for
  any other, None when the audit could not run); OpenBSD `pkg_add -u -n
  -v` (no security verdict). Base-system patches are one `base-system`
  entry, as decided in #799: OpenBSD's `syspatch -c`, and on a classic
  FreeBSD what `freebsd-update` has fetched; on pkgbase the base system is
  packages from FreeBSD-base.
- Services: get_services lists the enabled ones (FreeBSD `service ...
  status` as root, as root-only pidfiles hide daemons otherwise, without
  root when sudo refuses; OpenBSD `rcctl check`), manage_service runs
  start/stop/restart/enable/disable as root and returns success and
  output.

Fixtures recorded on the FreeBSD 15.1 and OpenBSD 7.9 VMs with genuinely
outdated packages (FreeBSD pointed at the latest branch, an OpenBSD
package taken back to its release build). Checked live on both, including
a service restart and installing and removing a package.

tests/fixtures/openbsd-vm/pkg_info_m.txt

@@ -0,0 +1,25 @@
+bash-5.3.9          GNU Bourne Again Shell
+bash-completion-2.17.0 programmable completion functions for bash
+e2fsprogs-1.47.3    utilities to manipulate ext2 filesystems
+meson-1.10.2v0      next-generation build system
+pcre2-10.44         perl-compatible regular expression library, version 2
+py3-configobj-5.0.9p0 config file reader and writer
+py3-jinja2-3.1.6p0  fast, optionally sandboxed, Python template engine
+py3-jsonpatch-1.33p2 library to apply JSON Patches according to RFC 6902
+py3-jsonschema-4.24.0 implementation of JSON Schema validation for Python
+py3-oauthlib-3.3.1  Python library for OAuth
+py3-packaging-26.0  core utilities for Python packaging
+py3-passlib-1.9.3p0 Python module providing a password hashing framework
+py3-requests-2.33.1 elegant and simple HTTP library for Python
+py3-responses-0.25.0p2 utility library for mocking out the `requests` Python
+py3-serial-3.5p0    serial interface class for Python
+py3-test-9.0.2p0    cross-project testing tool for Python
+py3-test-cov-7.1.0  pytest plugin for measuring coverage
+py3-test-mock-3.15.1 thin wrapper around mock package for easier use with pytest
+py3-test-xdist-3.8.0 py.test xdist plugin for distributed testing
+py3-tox-4.47.0      virtualenv-based automation of test activities
+py3-yaml-6.0.2p1    YAML parser and emitter in Python
+python-3.13.15p0    interpreted object-oriented programming language
+qemu-ga-10.2.1      QEMU guest agent
+quirks-7.194        exceptions to pkg_add rules
+sudo-1.9.17.2p1     execute a command as another user