Add ip2geo IP geolocation lookup

[bfzli]

Summary

• Adds a new IP address lookup for the ip2geo API
• Supports IPv4 and IPv6 geocoding
• Returns 30+ fields: city, country, continent, ASN, currency, flag, timezone, registered country, etc.
• Authentication via X-Api-Key header (auto-injected from api_key config)
• HTTPS only

Configuration

Geocoder.configure(
  ip_lookup: :ip2geo,
  api_key: "your-api-key"
)

result = Geocoder.search("134.201.250.155").first
result.city          # => "Los Angeles"
result.country       # => "United States"
result.coordinates   # => [34.0544, -118.244]
result.asn_number    # => 25876
result.currency_code # => "USD"

Files changed

• New: lib/geocoder/lookups/ip2geo.rb — lookup class
• New: lib/geocoder/results/ip2geo.rb — result class with 30+ accessors
• New: test/unit/lookups/ip2geo_test.rb — unit tests
• New: test/fixtures/ip2geo_8_8_8_8, test/fixtures/ip2geo_no_results — test fixtures
• Modified: lib/geocoder/lookup.rb — add :ip2geo to ip_services
• Modified: test/test_helper.rb — add lookup stub
• Modified: README_API_GUIDE.md — add documentation entry

Test plan

• Lookup loads and registers in ip_services
• Result class maps all fields correctly from API response
• Loopback/private IP handling works
• Live API test with real key returns correct data
• No new dependencies added