Add `sum_across_studies` to kda #1034

Job	Run time
Determine if CI should be skipped	7s
Corrector performance tests (ubuntu-latest, 3.8)	30m 40s
Unit tests (ubuntu-latest, 3.8)	35m 27s
Unit tests with minimum dependency versions (ubuntu-latest, 3.8)	27m 14s
Unit tests (ubuntu-latest, 3.9)	32m 43s
CBMR ImportError tests (ubuntu-latest, 3.8)	1m 0s
Estimator performance tests (ubuntu-latest, 3.8)	6m 54s
Unit tests (ubuntu-latest, 3.10)	32m 35s
Unit tests (ubuntu-latest, 3.11)	33m 46s
Smoke performance tests (ubuntu-latest, 3.8)	20m 55s
Unit tests (macos-latest, 3.8)	1h 9m 48s
Unit tests (macos-latest, 3.9)	40m 29s
Unit tests (macos-latest, 3.10)	38m 59s
Unit tests (macos-latest, 3.11)	36m 29s
Upload coverage	0s
	6h 47m 6s

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