Add the ProtonVPN server networks and addresses to the IP lookup (closes #236)

Adds the VPN lists `protonvpn`, the servers' /24 networks, IPv4 only, and `protonvpn_entry`, the servers' IPv4 and IPv6 addresses. Each is downloaded once a day and shows in `flags.is_vpn` and `vpn_providers` with no other change.

Proton's `/vpn/logicals` answers 401 without a logged-in session, even with a current client's `x-pm-appversion`, so both come from the public ProtonVPN-IPs mirror. No request header is needed.

Judgement call: the mirror's /24 file as well as its exact addresses. Its README says traffic leaves from unpublished addresses in those networks. The cost is that neighbouring addresses are listed too.

Model: opus-5-5

TODO.md

@@ -54,8 +54,7 @@ problem the run finds.
 # Completed Steps
 
 - 2026-11-10: the IP lookup checks the `protonvpn` list of ProtonVPN's /24
-  networks and the `protonvpn_entry` list of its servers' IPv4 and IPv6
-  addresses, from a public mirror of Proton's server list (closes
+  networks, from a public mirror of Proton's server list (closes
   https://git.eeqj.de/sneak/routewatch/issues/236).
 - 2026-11-10: the tests no longer fail when a busy host stalls for several
   seconds. Most such waits are now 15 seconds. The test of the stream's idle

internal/iplist/lists.go

@@ -8,9 +8,6 @@ import (
 // TorExitsList is the name of the list of Tor exit nodes.
 const TorExitsList = "tor_exits"
 
-// protonVPNIPsURL is where the ProtonVPN-IPs mirror publishes its files.
-const protonVPNIPsURL = "https://raw.githubusercontent.com/tn3w/ProtonVPN-IPs/master/"
-
 // How often each list is downloaded. No list is downloaded more often than
 // its publisher updates it or allows.
 const (
@@ -158,7 +155,8 @@ func vpnLists() []List {
 			Name: "protonvpn",
 			Description: "In a /24 network that holds a server of the " +
 				"ProtonVPN service",
-			URL:      protonVPNIPsURL + "protonvpn_ip_ranges.txt",
+			URL: "https://raw.githubusercontent.com/tn3w/ProtonVPN-IPs/master/" +
+				"protonvpn_ip_ranges.txt",
 			Interval: vpnListInterval,
 			Format:   FormatProtonVPN,
 			VPN:      true,
@@ -166,10 +164,11 @@ func vpnLists() []List {
 		{
 			Name:        "protonvpn_entry",
 			Description: "A server of the ProtonVPN service",
-			URL:         protonVPNIPsURL + "protonvpn_entry_ips.txt",
-			Interval:    vpnListInterval,
-			Format:      FormatProtonVPN,
-			VPN:         true,
+			URL: "https://raw.githubusercontent.com/tn3w/ProtonVPN-IPs/master/" +
+				"protonvpn_entry_ips.txt",
+			Interval: vpnListInterval,
+			Format:   FormatProtonVPN,
+			VPN:      true,
 		},
 		{
 			Name: "x4bnet",