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.

tests/fixtures/freebsd-host/COMMANDS.txt

@@ -0,0 +1,36 @@
+uname -a
+freebsd-version -kru
+cat /etc/os-release
+sysctl -n kern.hostname kern.ostype kern.osrelease kern.version
+sysctl -n hw.model hw.ncpu hw.physmem hw.machine_arch
+sysctl -n kern.boottime
+sysctl -n kern.smp.cpus vm.stats.vm.v_page_count vm.stats.vm.v_free_count vm.stats.vm.v_page_size
+kenv -q smbios.system.product smbios.system.serial smbios.system.maker smbios.bios.vendor
+uptime
+ifconfig -a
+netstat -rn
+netstat -rnW -f inet
+netstat -rnW -f inet6
+arp -an
+ndp -an
+sockstat -l -4 -6
+sockstat -l -4 -6 -P tcp,udp -q
+netstat -an -f inet
+pkg -N
+pkg info
+pkg query '%n\t%v\t%o\t%c'
+pkg version -vRL=
+service -e
+sysrc -a
+cat /etc/passwd
+ps -axww -o user,pid,ppid,%cpu,%mem,vsz,rss,stat,lstart,command
+crontab -l
+cat /etc/crontab
+df -k
+swapinfo -k
+kldstat
+which sudo doas python3 bash snmpd bsnmpd
+ls /usr/local/etc/rc.d /etc/rc.d
+cat /etc/rc.conf
+id
+cat /etc/group