Make test runner auto detect runnable tests

The current test runner requires each test file to be explicitly added to a list of tests in the run.lua file, this has created a point of pain when merging multiple branches together as it is common to have conflicts in this file. Change the runner to auto detect the tests needed to be run so we no longer get the merging issues.

Start by reading run.lua and tracing how the current explicit test list is assembled and executed. Run the existing test runner to establish its current behavior, then verify that runnable test files are discovered and executed without editing a central list, including when new test files are added.

Written by the indexing model from the issue text.