Add the iCloud Private Relay list to the IP lookup, with is_relay (closes #237)

Adds Apple's iCloud Private Relay egress list as `icloud_private_relay`, downloaded once a day, and `flags.is_relay`, true when an address is on it. Loaded, the list adds about 0.3 MiB to the Go heap; parsing it allocates about 94 MiB, freed by the next garbage collection.

Judgement call: a line with no comma fails the parse, so a plain network list served at Apple's URL cannot replace a good copy.

Model: opus-5-5

internal/iplist/lists.go

@@ -8,6 +8,10 @@ import (
 // TorExitsList is the name of the list of Tor exit nodes.
 const TorExitsList = "tor_exits"
 
+// ICloudPrivateRelayList is the name of the list of iCloud Private Relay's
+// networks.
+const ICloudPrivateRelayList = "icloud_private_relay"
+
 // protonVPNIPsURL is where the ProtonVPN-IPs mirror publishes its files.
 const protonVPNIPsURL = "https://raw.githubusercontent.com/tn3w/ProtonVPN-IPs/master/"
 
@@ -30,6 +34,9 @@ const (
 	fireHOLAbusersInterval = 5 * time.Hour
 	fireHOLLevel3Interval  = 3 * time.Hour
 
+	// Apple's iCloud Private Relay file is 12 MB, so once a day.
+	iCloudPrivateRelayInterval = 24 * time.Hour
+
 	// Spamhaus asks that DROP be downloaded at most once a day:
 	// https://www.spamhaus.org/blocklists/do-not-route-or-peer/
 	spamhausDROPInterval = 24 * time.Hour
@@ -84,6 +91,13 @@ func nonVPNLists() []List {
 			Interval: fireHOLLevel3Interval,
 			Format:   FormatLines,
 		},
+		{
+			Name:        ICloudPrivateRelayList,
+			Description: "In a network where iCloud Private Relay traffic leaves",
+			URL:         "https://mask-api.icloud.com/egress-ip-ranges.csv",
+			Interval:    iCloudPrivateRelayInterval,
+			Format:      FormatICloudPrivateRelayCSV,
+		},
 		{
 			Name: "spamhaus_drop",
 			Description: "In an IPv4 network that Spamhaus says spammers " +