Add nftables support with config generator and IP checker (#22)

* Add nftables support with config generator and IP checker

- Add generate_nft_blacklist.py for generating nftables configurations
- Add check_nft_blacklist.py for verifying IPs against blacklist
- Add blacklists_updater_nftables.sh for automated updates
- Add blacklists_nftables/ directory with generated configs
- Add GitHub Actions workflow for daily nftables updates
- Update README.md with nftables usage instructions

nftables is a modern replacement for iptables with better performance
and lower memory usage, especially for large rulesets. This addition
complements the existing iptables and nginx blacklist formats.

* Added nftables scripts help

blacklists_nftables/blacklist-v6.nft

@@ -0,0 +1,45 @@
+# Autogenerated nftables blacklist
+# Generated: 2026-01-12T09:09:02.010763Z
+# Source: /tmp/blacklist-v6.txt
+# IPv4: 0, IPv6: 17
+
+table inet filter {
+
+    set blacklist_v4 {
+        type ipv4_addr
+        flags interval
+    }
+
+    set blacklist_v6 {
+        type ipv6_addr
+        flags interval
+        elements = {
+            2a00:1148::/29,
+            2a00:46e0::/32,
+            2a00:a300::/32,
+            2a00:b4c0::/32,
+            2a00:bdc0::/33,
+            2a00:bdc0:8000::/34,
+            2a00:bdc0:c000::/35,
+            2a00:bdc0:e002::/47,
+            2a00:bdc0:e004::/47,
+            2a00:bdc0:e007::/48,
+            2a00:bdc0:f000::/36,
+            2a00:bdc1::/32,
+            2a00:bdc2::/31,
+            2a00:bdc4::/30,
+            2a14:25c0::/32,
+            2a14:25c5::/32,
+            2a14:25c6::/31
+        }
+    }
+
+    chain input {
+        type filter hook input priority 0;
+        policy accept;
+
+        ct state { established, related } accept
+
+        ip6 saddr @blacklist_v6 counter drop
+    }
+}