Add feature to support custom `now_utc` implementations #5023

Job	Run time
check-for-run-condition	1s
check-for-modification	6s
build-wasm / build-wasm (ubuntu-latest)	10m 50s
build-and-test (ubuntu-latest)	6m 8s
build-and-test (macos-latest)	4m 30s
build-and-test (windows-latest)	15m 5s
test-wasm-firefox (ubuntu-latest)	2m 52s
test-wasm-chrome (ubuntu-latest)	4m 18s
test-wasm (ubuntu-latest)	2m 27s
	46m 17s

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