perf: speed-up track_shard_column_pos()

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/transformation/redistribution.rs

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

...ad-core/src/ir/transformation/redistribution/left_join.rs