feat: use geoip string as IP directly, skip publicIP lookup

[softko]

The geoip option already accepts string | boolean in the TypeScript type definition (matching the Python API), but the implementation always called publicIP() to resolve the address — ignoring any string value passed by the caller.

Changes:

• If geoip is a valid IP string, it is used directly for geolocation lookup — no outbound request is made to resolve the public IP
• If geoip is true, behavior is unchanged: the public IP is resolved automatically (via the proxy if one is set)
• Invalid IP strings are caught by the existing validateIP call inside getGeolocation

This brings the JS implementation in line with the Python version's documented behavior:
Pass the target IP address to use, or true to find the IP address automatically.

[barjin]

Lgtm, thank you for your contribution @softko !