feat: Use CURL multi. #2484

Job	Run time
build-test-curl	5m 52s
contract-tests	2m 41s
contract-tests-curl	3m 7s
build-test-client-windows-curl	9m 19s
build-test-client-mac-curl	7m 46s
build-test	5m 40s
build-test-client-mac	7m 15s
build-test-client-windows	15m 37s
	57m 17s

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