Module mocking breaks top level requires in other test suites

[Derpius]

Context

When mocking a module with lest outside of a test function, the mock is applied immediately when the file is initially loaded to register tests.

This causes calls to require, loadfile, and dofile at the top level / describe level of other test suites to be mocked, but the mock should be scoped to the file where the mock was added.

Solution

To solve this we need to store mocks separately for each file in the runtime, then use them only while scanning the file for tests, and while running the tests in that file.