tapdb: fix performance of aggregate stats #3741

Job	Run time
Docker build check	3m 39s
Docker build check	3m 39s
cross compilation	15m 55s
cross compilation	15m 55s
Compilation check	5m 2s
Compilation check	5m 2s
Format check	2m 37s
Format check	2m 37s
run itests	15m 12s
run itests	15m 12s
run itests postgres	23m 22s
run itests postgres	23m 22s
Lint check	6m 2s
Lint check	6m 2s
migration version check	14s
migration version check	14s
go mod check	2m 32s
go mod check	2m 32s
RPC check	3m 31s
RPC check	3m 31s
run LiT tests	18m 54s
run LiT tests	18m 54s
sample configuration check	3m 55s
sample configuration check	3m 55s
Sqlc check	4m 56s
Sqlc check	4m 56s
test vector check	4m 25s
test vector check	4m 25s
run unit tests (unit-race)	15m 5s
run unit tests (unit-race)	15m 5s
run unit tests (unit-cover)	7m 20s
run unit tests (unit-cover)	7m 20s
run unit tests (unit dbbackend=postgres)	6m 15s
run unit tests (unit dbbackend=postgres)	6m 15s
finish	2s
finish	25s
	4h 38m 19s

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