Add `sum_across_studies` to kda #1029

Job	Run time
Determine if CI should be skipped	4s
Corrector performance tests (ubuntu-latest, 3.8)	31m 4s
Estimator performance tests (ubuntu-latest, 3.8)	6m 45s
Unit tests with minimum dependency versions (ubuntu-latest, 3.8)	28m 19s
Unit tests (ubuntu-latest, 3.8)	33m 43s
CBMR ImportError tests (ubuntu-latest, 3.8)	59s
Unit tests (ubuntu-latest, 3.9)	35m 26s
Smoke performance tests (ubuntu-latest, 3.8)	20m 55s
Unit tests (ubuntu-latest, 3.10)	37m 43s
Unit tests (ubuntu-latest, 3.11)	35m 47s
Unit tests (macos-latest, 3.8)	37m 50s
Unit tests (macos-latest, 3.9)	37m 50s
Unit tests (macos-latest, 3.10)	37m 42s
Unit tests (macos-latest, 3.11)	37m 51s
Upload coverage	1s
	6h 21m 59s

Provide feedback