feat: FreeBSD and OpenBSD drivers, read side

FreeBSDDriver (`freebsd`) and OpenBSDDriver (`openbsd`) on a shared
BsdDriver, for the BSD VMs netOrk provisions and BSD hosts added by hand
(NetOrk/netork#798).

- SSH over exec channels (napalm-device-types' run_on_transport): no PTY,
  stdout and stderr apart, real exit codes; run_command()/open_stream()
  are public. Root through `sudo -S` with the password on stdin, or
  `sudo -n` without one.
- Facts: hostname, release and running kernel (freebsd-version / uname),
  hardware from SMBIOS (kenv) or hw.* sysctls, uptime from kern.boottime.
- Interfaces and addresses (ifconfig -a: ether/lladdr, hex netmasks,
  scoped IPv6), routes (netstat -rn, OpenBSD's abbreviated networks
  written out, host/broadcast/loopback entries left out), ARP (FreeBSD's
  sentences, OpenBSD's table), users and groups, processes (lstart read as
  one five-word field), cron jobs (system crontab and the login user's).
- Parsers are pure functions, tested on output recorded from FreeBSD 15.1
  (hand-installed and cloud image) and OpenBSD 7.9 (NetOrk/netork#793),
  with internal addresses replaced by documentation ranges.

CHANGELOG.md

@@ -0,0 +1,20 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+- `FreeBSDDriver` (`freebsd`) and `OpenBSDDriver` (`openbsd`) on a shared
+  `BsdDriver`: SSH over exec channels (no PTY, real exit codes), root through
+  `sudo -S` with the password on stdin.
+- Read side (NetOrk/netork#798): facts (SMBIOS through `kenv` on FreeBSD,
+  `hw.*` sysctls on OpenBSD; uptime from `kern.boottime`), interfaces and
+  their addresses (`ifconfig -a`), routes (`netstat -rn`), ARP (`arp -an`),
+  users and groups, processes (`ps … lstart`), cron jobs (system crontab and
+  the login user's).
+- Parsers tested on output recorded from FreeBSD 15.1 (hand-installed and
+  cloud image) and OpenBSD 7.9 (NetOrk/netork#793).