feat: impl `OwnedTablePostprocessingStep` for `GroupByPostprocessing`… #73

Job	Run time
lint-and-test / Test Suite	10m 17s
lint-and-test / Clippy	1m 19s
lint-and-test / Check Package	2m 50s
lint-and-test / Format	26s
lint-and-test / Unused Dependencies	6m 42s
Release	2m 36s
	24m 10s

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