process_registry_updates without a full copy of the validator set #14130
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What type of PR is this?
Bug fix
What does this PR do? Why is it needed?
state.Validators() is a full copy of 1M+ validators. By using a series of validator index slices, we can reduce the worst case copy to ~8M bytes ~= 8Mb of indices to process.
The average case is near zero allocation.
Special shoutout to @terencechain for the idea and the debugging of my implementation.
Soft requirement for #14005.
Which issues(s) does this PR fix?
Other notes for review
I moved sortableIndices to its own file and added unit tests for this specifically. The lack of unit tests on this struct cost us nearly a full day of debugging a silly mistake.