Fix chunk calculation for hybrid aggregation #539

Job	Run time
Basic Checks	19m 42s
Additional Builds and Concurrency Tests	14m 9s
Measure coverage	27m 12s
miri	3m 2s
Release builds and tests	10m 52s
sanitize (address)	18m 3s
Slow tests	20m 3s
sanitize (address, multi-threading)	19m 26s
sanitize (leak)	7m 56s
sanitize (leak, multi-threading)	8m 23s
	2h 28m 48s

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