port: Kludge together `WhenceUniverse::save()` support, for native JS… #190

Job	Run time
miri	2m 53s
no_std	40s
build (ubuntu, stable, locked, true)	1h 9m 47s
build (windows, stable, locked, false)	26m 58s
build (macos, stable, locked, false)	36m 11s
build (ubuntu, nightly, locked, false)	19m 19s
build (ubuntu, beta, locked, false)	17m 38s
build (ubuntu, stable, latest, false)	20m 22s
build (ubuntu, stable, minimal, false)	32m 30s
deploy	6s
fuzz	17m 54s
	4h 4m 18s

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