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As we found out in #18870, `andArityType` is not monotone, with potentially severe consequences for termination of fixed-point iteration. That showed in an abundance of "Exciting arity" DEBUG messages that are emitted whenever we do more than one step in fixed-point iteration. The solution necessitates also recording `OneShotInfo` info for `ABot` arity type. Thus we get the following definition for `ArityType`: ``` data ArityType = AT [OneShotInfo] Divergence ``` The majority of changes in this patch are the result of refactoring use sites of `ArityType` to match the new definition. The regression test `T18870` asserts that we indeed don't emit any DEBUG output anymore for a function where we previously would have. Similarly, there's a regression test `T18937` for #18937, which we expect to be broken for now. Fixes #18870.
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