feat: Use CURL multi. #2486

Job	Run time
contract-tests	2m 43s
contract-tests-curl	2m 44s
build-test-curl	5m 33s
build-test	5m 28s
build-test-client-windows	16m 19s
build-test-client-mac	6m 40s
build-test-client-mac-curl	7m 26s
build-test-client-windows-curl	9m 41s
	56m 34s

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