Bug Report: EXISTS subqueries no longer apply LIMIT 1

[arthurschreiber]

Overview of the Issue

When subqueries were moved to the operator model, Vitess stopped applying LIMIT 1 on EXISTS subqueries.

See the comment in https://github.com/vitessio/vitess/pull/13750/files#r1337276087, and the surrounding test case changes for examples where the optimization was lost. It'd be great to bring this optimization back to ensure we don't end up loading thousands of rows when we already know the result as soon as the first row is returned.

Reproduction Steps

N/A

Binary Version

v18 and later

Operating System and Environment details

N/A

Log Fragments

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