Move tests in `lib/soro_gps` to `tests/` directory

[onkoe]

These tests should be moved to another file for testing at some point. We can make an issue for this.

For info on how to make integration tests for Rust, see: https://doc.rust-lang.org/book/ch11-03-test-organization.html

Originally posted by @logbasem in #151 (comment)