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.

napalm_bsd/__init__.py

@@ -0,0 +1,6 @@
+"""NAPALM drivers for BSD hosts: FreeBSD and OpenBSD, over SSH."""
+
+from napalm_bsd.freebsd import FreeBSDDriver
+from napalm_bsd.openbsd import OpenBSDDriver
+
+__all__ = ["FreeBSDDriver", "OpenBSDDriver"]