[TEST] Add test linear_past_eltwise_add when the graph has multiple joins where to apply the transformation (was failing in this case) plu test moving linear tensor ops, not only scalar ones

turns out there was a problem with signed values after all
failing testcases with k=5 produce the indices of positive values correctly, but negative ones don't seem to be compared correctly (always producing index 0?)

[TEST] Add test linear move_add_past_mul for non_linear graphs and improve previous test by checking if doing job

this changed in the latest Brevitas export