feat: Use CURL multi. #2481

Job	Run time
contract-tests-curl	2m 41s
contract-tests	2m 46s
build-test	5m 26s
build-test-client-windows-curl	9m 17s
build-test-client-mac	11m 47s
build-test-client-windows	15m 56s
build-test-client-mac-curl	11m 53s
build-test-curl	5m 42s
	1h 5m 28s

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