Add `sum_across_studies` to kda #1030

Job	Run time
Determine if CI should be skipped	3s
Corrector performance tests (ubuntu-latest, 3.8)	1m 15s
Unit tests (ubuntu-latest, 3.8)	1m 17s
Unit tests (ubuntu-latest, 3.9)	1m 15s
Unit tests with minimum dependency versions (ubuntu-latest, 3.8)	1m 17s
CBMR ImportError tests (ubuntu-latest, 3.8)	1m 0s
Estimator performance tests (ubuntu-latest, 3.8)	1m 16s
Unit tests (ubuntu-latest, 3.10)	1m 16s
Unit tests (ubuntu-latest, 3.11)	1m 15s
Smoke performance tests (ubuntu-latest, 3.8)	1m 15s
Unit tests (macos-latest, 3.8)	1m 17s
Unit tests (macos-latest, 3.9)	1m 16s
Unit tests (macos-latest, 3.10)	1m 17s
Unit tests (macos-latest, 3.11)	1m 16s
Upload coverage	1s
	16m 16s

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