feat: add incremental log scanning with resumable byte offsets

Track last processed byte offset per log file so scans only read new
entries, add --full flag to force a rescan, and persist state atomically.

data/whois_cache.json

@@ -966,5 +966,9 @@
   "185.198.240.238": "185.198.240.0/24",
   "34.125.213.146": "34.125.208.0/20",
   "222.176.200.21": "222.176.0.0/13",
-  "106.117.109.102": "106.117.0.0/16"
+  "106.117.109.102": "106.117.0.0/16",
+  "121.29.51.109": "121.28.0.0/15",
+  "74.248.97.169": "74.248.0.0/15",
+  "34.176.154.83": "34.176.144.0/20",
+  "35.196.132.85": "35.196.128.0/20"
 }