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/openbsd-vm/COMMANDS.txt

@@ -0,0 +1,32 @@
+uname -a
+sysctl -n kern.hostname kern.ostype kern.osrelease kern.version
+sysctl -n hw.model hw.ncpu hw.physmem hw.vendor hw.product hw.serialno hw.uuid
+sysctl -n kern.boottime
+uptime
+ifconfig -a
+netstat -rn
+netstat -rn -f inet
+netstat -rn -f inet6
+arp -an
+ndp -an
+netstat -an -f inet
+netstat -an -f inet6
+sudo fstat -n | head -60
+pkg_info
+pkg_info -q
+sudo pkg_add -u -n
+sudo syspatch -c
+sudo syspatch -l
+rcctl ls on
+rcctl ls started
+rcctl ls failed
+cat /etc/passwd
+ps -axww -o user,pid,ppid,%cpu,%mem,vsz,rss,stat,lstart,command
+cat /etc/crontab
+sudo crontab -l
+df -k
+swapctl -l
+sysctl -n vm.loadavg
+which snmpd
+cat /etc/rc.conf.local
+id