feat: Use CURL multi. #2483

Job	Run time
contract-tests-curl	3m 4s
contract-tests	2m 40s
build-test	5m 18s
build-test-client-windows	15m 58s
build-test-client-mac	12m 11s
build-test-client-mac-curl	5m 21s
build-test-curl	5m 47s
build-test-client-windows-curl	14m 56s
	1h 5m 15s

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