Initial scaffold for tomswall

Spiritual successor to shorewall — manages nftables directly via
google/nftables. Reads a single YAML config covering zones, interfaces,
hosts, policy, rules, snat, and named portgroups. Computes differential
changes against the running nftables state and applies them atomically.
Supports detecting and purging rules added outside of tomswall.

.gitignore

@@ -0,0 +1,2 @@
+tomswall
+*.test