feat: Use CURL multi. #2487

Job	Run time
contract-tests	2m 39s
contract-tests-curl	3m 0s
build-test-client-windows-curl	9m 15s
build-test-client-windows	16m 6s
build-test-client-mac-curl	8m 20s
build-test	5m 12s
build-test-client-mac	10m 50s
build-test-curl	5m 44s
	1h 1m 6s

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