This PR is purely for improved readability; I was doing work involving
the file and think this may help others who are trying to understand
what's going on.
1. `snapshot.Tree.Rebuild()` now returns a function that blocks until
regeneration is complete, allowing `Tree.waitBuild()` to be removed
entirely as all it did was search for the `done` channel behind this new
function.
2. Its usage inside `New()` is also simplified by (a) only waiting if
`!AsyncBuild`; and (b) avoiding the double negative of `if !NoBuild`.
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Co-authored-by: Martin HS <martin@swende.se>
23800122b3