HHH-18992 - a few changes/additions to the MultiLoadLockingTest

- added an @AfterEach tearDown method
- added tests also for findMultiple and byMultipleNaturalId
- corrected the tests that use optimistic/optimistic_force_increment
  (they should use a versioned entity)
- add statement inspection where applicable

Signed-off-by: Jan Schatteman <[email protected]>

Author: jrenaat