refactor PLT-1.1 helper methods

[dplore]

There should be a single _test.go file in a folder.

The base_test.go file is all helper methods. Please move the helper functions inside /internal. For example functions related to platform probably could go into a library that's already started at: internal/components/components.go. Similarly different location for IP address incrementing function (inside /internal)

[dplore]

Also note I see this test README which heavily overlaps with PLT-1.1. This RT-8 test README should be removed

https://github.com/openconfig/featureprofiles/blob/main/feature/interface/singleton/singleton_with_breakouts/README.md