feat: add missing PlusAnonymous fields and fix PlusMobile

[rbarrielabrystech]

Summary

• PlusAnonymous: Add IsResProxy, LastSeen, and PercentDaysSeen fields to match the IPinfo Max /lookup API response
• PlusMobile: Replace incorrect Name field with CountryCode to match actual API response schema

Context

The IPinfo Max /lookup endpoint returns these fields in the anonymous object:

{
  "anonymous": {
    "is_proxy": false,
    "is_relay": false,
    "is_tor": false,
    "is_vpn": true,
    "is_res_proxy": true,
    "name": "NetNut",
    "last_seen": "2026-03-12",
    "percent_days_seen": 100
  }
}

The current PlusAnonymous struct only captures 5 of these 8 fields. The missing fields (is_res_proxy, last_seen, percent_days_seen) are silently dropped during JSON unmarshaling.

Similarly, PlusMobile.Name doesn't exist in the API response — the actual field is country_code.

Changes

1. ipinfo/plus.go: Added 3 new fields to PlusAnonymous, replaced Name with CountryCode in PlusMobile
2. example/lookup-plus/main.go: Updated example to demonstrate the new fields

Testing

• Tested against live IPinfo Max API — all new fields correctly populated
• go build ./... passes cleanly
• Backwards compatible for PlusAnonymous; PlusMobile.Name → .CountryCode is a correctness fix (Name was always empty)