Restart node building if previous dep is dirty, fix check-then-act races

While initializing the SkyFunctionEnvironment for a node being built, if
a previously requested dep is found to be not done, reset and re-enqueue
the building node. This lets the node handle the not-done dep like any
other not-done dep (e.g. by enqueuing it or by waiting to be signalled
by it).

Similarly, while registering newly requested deps when building a node
yields a value or an error, if a newly requested dep is found to be not
done, return without completing the node, so that it may be signalled by
the dep (without crashing; done nodes cannot be signalled).

Also fixes a handful of remaining check-then-act races during Skyframe
evaluation that were vulnerable to done->dirty node transitions.

(Note that done->dirty node transitions during evaluation are planned,
but not yet possible.)

RELNOTES: None.
PiperOrigin-RevId: 202886360

0 files changed, 0 insertions, 0 deletions