feat: a public command channel; no warnings of its own (0.4.0)

run_command and open_stream (napalm-device-types CommandChannelMixin,
which AccessPointDriver carries) run on an SSH exec channel next to
netmiko's shell: stdin, stderr apart, a real exit code. netOrk sent UCI
scripts and the wifi channel through the private _send_command, typing
a file in base64 chunks or printf lines; with stdin it writes it with
cat, and base64 is needed for nothing (netOrk #1113). OpenWrt has no
sudo, so a privileged command from a login other than root is refused
before it runs.

get_device_warnings goes with it: no_base64 was its last code.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "napalm-openwrt"
-version = "0.3.0"
+version = "0.4.0"
 description = "NAPALM driver for OpenWrt routers/access-points"
 readme = "README.md"
 license = { text = "Apache-2.0" }