Update GeoIP handling and POST query functionality

The code updates significantly improve the handling of GeoIP data across several functions. In particular, synchronization has been introduced in GeoIP handling to ensure thread safety during data access. Additionally, automatic GeoIP database reloading is now performed every 300 seconds via a new goroutine. POST query functionality is also updated to return the client's IP address and corresponding country. The updates aim to enhance reliability and resource efficiency.