Overhaul the logic and method names involved in enabling and disabling
reference caching in `TupleTree<T>`. `TupleTreeReference<T, U>` now
lazily caches the target and will traverse the path only when needed.
Also expose and use these functions in the new pipeline, which should
provide some speedup when executing a `Schedule`.
`TupleTreeReference`s use the Root type as a pointer only so they can
operate with forward declarations. Before this commit there were static
asserts that prevented this use case, and thus required the headers
defining the root type to be included before this one to work correctly.
We drop those `static_assert`s to make sure that all headers are parsable
on their own.
Now all the generated `.cpp` include `Binary.h`. This ensures we don't
trigger the wrong concept due to forward declarations.
Also, this commit introduces a couple of `static_assert`s which should
enable us to early identification of similar problems.
Giacomo Vercesi