Add `sum_across_studies` to kda #1032

Job	Run time
Determine if CI should be skipped	4s
Estimator performance tests (ubuntu-latest, 3.8)	6m 54s
Unit tests (ubuntu-latest, 3.8)	11m 7s
Unit tests with minimum dependency versions (ubuntu-latest, 3.8)	11m 7s
Unit tests (ubuntu-latest, 3.9)	11m 4s
Corrector performance tests (ubuntu-latest, 3.8)	11m 8s
Unit tests (ubuntu-latest, 3.10)	11m 7s
Smoke performance tests (ubuntu-latest, 3.8)	11m 7s
CBMR ImportError tests (ubuntu-latest, 3.8)	1m 1s
Unit tests (ubuntu-latest, 3.11)	11m 6s
Unit tests (macos-latest, 3.8)	11m 1s
Unit tests (macos-latest, 3.9)	11m 7s
Unit tests (macos-latest, 3.10)	11m 6s
Unit tests (macos-latest, 3.11)	11m 7s
Upload coverage	1s
	2h 10m 7s

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