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/netstat_rnW_f_inet6.txt

@@ -0,0 +1,13 @@
+Routing tables
+
+Internet6:
+Destination                       Gateway                       Flags   Nhop#    Mtu            Netif Expire
+::/96                             link#2                        URS         6  16384              lo0
+::1                               link#2                        UHS         1  16384              lo0
+::ffff:0.0.0.0/96                 link#2                        URS         6  16384              lo0
+fe80::%lo0/10                     link#2                        URS         6  16384              lo0
+fe80::%em0/64                     link#1                        U           5   1500              em0
+fe80::be24:11ff:fe20:b020%lo0     link#2                        UHS         4  16384              lo0
+fe80::%lo0/64                     link#2                        U           3  16384              lo0
+fe80::1%lo0                       link#2                        UHS         2  16384              lo0
+ff02::/16                         link#2                        URS         6  16384              lo0