Draft: DAL/Test: fail if observer does not receive all the expected shards

What and why

This MR is about the amplification_without_lost_shards test. This test exercises the amplification cancellation feature introduced in !12566 (merged). It consists in a slot producer DAL node directly connected to an observer DAL node, the slot producer produces a slot and sends all the shards to the observer. We observe that a reconstruction is planned by the observer and then cancelled.

Because some shards were sometimes dropped by the observer node, the test was flaky. MR !12592 (merged) weakens the test to avoid the flakyness by allowing the case were shards are missing and the reconstruction actually happens.

I expect !13151 (merged) to have fixed this problem.

This MR makes the amplification_without_lost_shards test stricter. Basically, I reverted !12592 (merged) except that we still end the test as soon as the reconstruction terminates but instead of ending the test successfully we now fail in this case.

How

Manually testing the MR

Run the following command a few times to be sure the test is not flaky:

dune exec tezt/tests/main.exe -- alpha dal amplification --skip 1

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR