rebase && review fixes

sbroad-core/src/executor/engine/helpers.rs

sbroad-core/src/executor/engine/mock.rs

sbroad-core/src/frontend/sql/ir/tests.rs

sbroad-core/src/ir/distribution.rs

sbroad-core/src/ir/relation.rs

sbroad-core/src/ir/relation/tests.rs

sbroad-core/src/ir/transformation/redistribution.rs

...tifactory/backend/sql/tree/arbitrary_projection_plan.yaml

...ifactory/backend/sql/tree/arithmetic_projection_plan.yaml

...tifactory/backend/sql/tree/arithmetic_selection_plan.yaml

...sts/artifactory/backend/sql/tree/sql_order_selection.yaml

...re/tests/artifactory/ir/distribution/join_unite_keys.yaml

.../tests/artifactory/ir/distribution/shrink_dist_key_1.yaml

.../tests/artifactory/ir/distribution/shrink_dist_key_2.yaml

...e/tests/artifactory/ir/distribution/shuffle_dist_key.yaml

...artifactory/ir/distribution/union_fallback_to_random.yaml

...ests/artifactory/ir/distribution/union_preserve_dist.yaml

sbroad-core/tests/artifactory/ir/operator/join.yaml

...ad-core/tests/artifactory/ir/operator/output_aliases.yaml

...ts/artifactory/ir/operator/output_aliases_duplicates.yaml