feat: Use CURL multi. #1504

Job	Run time
contract-tests-curl	1m 48s
build-test-server-curl	1m 38s
build-test-server	6m 30s
contract-tests	3m 34s
build-test-server-mac-curl	11m 43s
build-test-server-mac	8m 40s
build-test-server-windows-curl	7m 55s
build-test-server-windows	18m 29s
	1h 0m 17s

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