Refactor RFQ BuyOrder struct #3318

Job	Run time
Format check	26s
Compilation check	50s
Docker build check	3m 38s
cross compilation	5m 21s
run itests	8m 49s
run itests postgres	17m 0s
Lint check	2m 47s
migration version check	10s
go mod check	22s
RPC check	1m 11s
run LiT tests	11m 10s
sample configuration check	40s
Sqlc check	2m 41s
test vector check	53s
run unit tests (unit-race)	7m 44s
run unit tests (unit-cover)	2m 54s
run unit tests (unit dbbackend=postgres)	5m 18s
finish	4s
	1h 11m 58s

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