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-vm/cat_etc_crontab.txt

@@ -0,0 +1,22 @@
+# /etc/crontab - system crontab for FreeBSD
+#
+#
+SHELL=/bin/sh
+PATH=/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin
+#
+#minute	hour	mday	month	wday	who	command
+#
+# Save some entropy so that /dev/random can re-seed on boot.
+*/11	*	*	*	*	operator /usr/libexec/save-entropy
+#
+# Rotate log files every hour, if necessary.
+0	*	*	*	*	root	newsyslog
+#
+# Perform daily/weekly/monthly maintenance.
+1	3	*	*	*	root	periodic daily
+15	4	*	*	6	root	periodic weekly
+30	5	1	*	*	root	periodic monthly
+#
+# Adjust the time zone if the CMOS clock keeps local time, as opposed to
+# UTC time.  See adjkerntz(8) for details.
+1,31	0-5	*	*	*	root	adjkerntz -a