Stream/Spliterator support for RunList

[basil]

RunList, despite its name, is best used as an Iterable rather than a Collection, because operations like Collection#size trigger eager loading of all build records. Despite this, RunList#stream triggers eager loading of all builds, not only because it does not plumb through the corresponding stream() and spliterator() calls to the underlying AbstractLazyLoadRunMap, but also because AbstractLazyLoadRunMap's own entrySet(), keySet(), and values() methods return objects whose Spliterators are sized and therefore incompatible with lazy-loading. This change updates those methods to return Spliterators of unknown size, which do not trigger eager loading. As a bonus, we also update AbstractLazyLoadRunMap#keySet so that its return value's Spliterator has the Spliterator.SORTED characteristic and a corresponding Comparator (which is appropriate because AbstractLazyLoadRunMap implements SortedMap). I have added new tests covering all of this functionality, including verifying lazy-loading behavior with RunLoadCounter. The tests fail without the changes to core/src/main and pass with them.

Proposed changelog entries

• Improve performance by lazy loading build records from the run list.

Proposed upgrade guidelines

N/A

Submitter checklist

• (If applicable) Jira issue is well described
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Desired reviewers

@mention

Maintainer checklist

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[jglick]

verifying lazy-loading behavior with RunLoadCounter. The tests fail without the changes to core/src/main and pass with them

These are the magic words!

[oleg-nenashev]

Looks good! Looking forward to see how it behaves on performance metrics