feat: allow duplicate column names in IR node output

sbroad-core/src/backend/sql/tree/tests.rs

sbroad-core/src/executor/tests/frontend.rs

sbroad-core/src/frontend/sql.rs

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

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

sbroad-core/src/ir.rs

sbroad-core/src/ir/aggregates.rs

sbroad-core/src/ir/expression.rs

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

sbroad-core/src/ir/operator.rs

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

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

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

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

...ore/src/ir/transformation/redistribution/tests/segment.rs

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

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