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/df_k.txt

@@ -0,0 +1,10 @@
+Filesystem  1K-blocks      Used     Avail Capacity  Mounted on
+/dev/sd0a      148590    132976      8186    95%    /
+/dev/sd0k    11284654        38  10720384     1%    /home
+/dev/sd0e     1633278        14   1551602     1%    /tmp
+/dev/sd0d     2468798   1562784    782576    67%    /usr
+/dev/sd0g      948974    277644    623882    31%    /usr/X11R6
+/dev/sd0h     2912174    299670   2466896    11%    /usr/local
+/dev/sd0j     5831982         2   5540382     1%    /usr/obj
+/dev/sd0i     2404686         2   2284450     1%    /usr/src
+/dev/sd0f     2546942     10948   2408648     1%    /var