Add fixed-point `WithinTolerance` method and greater-than operators #3202

Job	Run time
cross compilation	5m 34s
Format check	3m 29s
Docker build check	3m 17s
Compilation check	4m 54s
run itests	12m 59s
run itests postgres	20m 20s
Lint check	6m 52s
migration version check	14s
go mod check	53s
RPC check	4m 17s
run LiT tests	15m 59s
sample configuration check	4m 31s
Sqlc check	49s
test vector check	4m 47s
run unit tests (unit-race)	7m 45s
run unit tests (unit-cover)	7m 23s
run unit tests (unit dbbackend=postgres)	5m 31s
finish	3s
	1h 49m 37s

Provide feedback