don't test with bipolar datatype, must support zero
merged rtlsim and cppsim into a single parametrized test

This reverts commit 2e96d065.

[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?)