feat: Use CURL multi. #1507

Job	Run time
contract-tests-curl	3m 36s
contract-tests	3m 32s
build-test-server	6m 41s
build-test-server-mac-curl	11m 32s
build-test-server-mac	9m 33s
build-test-server-windows	18m 42s
build-test-server-windows-curl	19m 19s
build-test-server-curl	6m 30s
	1h 19m 25s

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