Unify the clean-up testing tools with the sandbox
A sandbox utility is dedicated to cleaning up the unit test-related side effects but handles only the newly created files. We also have separate utilities to support replacing global variables and reverting environment variable changes. We can unify all these functions to create a universal tool for cleanup. Currently, the developer must know and remember each utility and call it correctly. It causes us sometimes to write the test-scope functions to clean up because we forget that the solution already exists. An all-in-one tool would allow us to write more consistent and idiomatic code.