feat: get_host_firewall, the host's own netfilter rules (NetOrk/netork#1344)

Mixes in napalm-device-types' HostFirewallMixin. The transport runs the shared
read-only command as root on an exec channel: nft prints the whole ruleset as
one line of JSON, longer than the PTY takes reliably, and both nft and
iptables-save need CAP_NET_ADMIN. Requires napalm-device-types 4.21.0;
version 0.13.0.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "napalm-linux"
-version = "0.12.0"
+version = "0.13.0"
 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>=4.20.0",
+    "napalm-device-types>=4.21.0",
     "netmiko>=4.0.0",
     "paramiko>=5.0.0",  # CVE-2026-44405
 ]