feat: Use CURL multi. #2493

Job	Run time
build-test	5m 33s
contract-tests-curl	2m 53s
build-test-curl	5m 41s
contract-tests	2m 52s
build-test-client-windows-curl	8m 50s
build-test-client-mac	8m 43s
build-test-client-windows	16m 23s
build-test-client-mac-curl	6m 11s
	57m 6s

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