Single-pass test planning

[Paul S.]

We might significantly simplify the test planner if using the following approach:

1. Everything is memoized by default
2. The user specifies "forking points" - non-memoized components, all the subgraphs after these components must be instantiated per test

This way we should be able to complete test planning in a single pass and the odd concept of memoization levels would be gone.