refactor: Implement cancellation for Delay() timers. (#524) #2798

Job	Run time
build-test-curl	6m 20s
contract-tests	3m 24s
build-test-client-mac-curl	4m 29s
build-test-client-windows-curl	14m 30s
build-test-client-mac	5m 19s
build-test	6m 3s
build-test-client-windows	14m 34s
contract-tests-curl	3m 32s
	58m 11s

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