At least these tests leak:

1) Atk4\Ui\Tests\CallbackTest::testCallback
Memory leak detected! (8.918 MB + 0.47 MB + 16.328 KB, 1 iterations)

2) Atk4\Ui\Tests\CallbackTest::testViewUrlCallback
Memory leak detected! (9.452 MB + 0.041 MB + 35.227 KB, 1 iterations)

3) Atk4\Ui\Tests\FormTest::testSubmitError
Memory leak detected! (11.507 MB + 0.127 MB + 0.188 KB, 1 iterations)

tested with 1k iterations.

Observations:

• repeated require does not leak (tested with 100k include calls)
• but only if it does not include an anonymous class (new class() {}; is enough, even if never used)
• anonymous functions does no leak (even in complex such $fx = function() use ($bar) { return $bar; };)
• not leaky if included multiple times, but not evaluated - https://3v4l.org/R6f8k
• Fix all memory leaks #1672 pass with higher iteration count (about 100+) only on PHP 8.1+ with opcache enabled