feat: apt's proxy through AptProxyMixin (NetOrk/netork#1397)

get_package_proxy() is what apt-config dump says, not 00proxy alone: a
proxy in 90curtin-aptproxy or /etc/apt/apt.conf wins over it and was
missed. The driver now supplies only the transports: reads on the exec
channel, root commands through _root_outcome, the file through the staged
_install_file_as_root. New: get_package_proxy_report() and
check_package_proxy(). configure_package_proxy() also comments out other
proxy lines, reads the result back and fetches through the proxy.

Requires napalm-device-types 4.22.0; version 0.14.0.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "napalm-linux"
-version = "0.13.0"
+version = "0.14.0"
 description = "NAPALM driver for generic Linux systems via SSH"
 readme = "README.md"
 requires-python = ">=3.9"
@@ -37,7 +37,7 @@ classifiers = [
 ]
 dependencies = [
     "napalm>=4.0",
-    "napalm-device-types>=4.21.0",
+    "napalm-device-types>=4.22.0",
     "netmiko>=4.0.0",
     "paramiko>=5.0.0",  # CVE-2026-44405
 ]