Fix DAL reward test

What

Fix test Alpha: Testing DAL node (attesters receive DAL rewards) to make it pass.

Why

This test was flaky. Some discussion about it arised in !16049 (merged).

How

The failure of the test was due to asynchrony between the nodes. Hence, we now force the DAL node to publish commitment, and let it compute the counter rather than trying to anticipate the number of time a commitment has already been published.

Manually testing the MR

Running:

make && dune exec -- tezt/tests/main.exe --verbose --file tezt/tests/dal.ml --title 'Alpha: Testing DAL node (attesters receive DAL rewards)' --log-file /tmp/tezt3.txt

should pass everytime you try it.