Swift

Fixed `ObservableObject` conformance for `PersistentContainerStorage` #94

Job	Run time
macOS (debug, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	1m 56s
macOS (release)	7m 53s
macOS (release, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	11m 19s
Android (6.1, x86_64)	3m 45s
Android (nightly-6.2, x86_64)	3m 39s
Linux (swift:6.0.3, debug)	1m 52s
Linux (swift:6.1.2, release)	12m 27s
Linux (swift:6.1.2, debug)	1m 51s
Linux (swift:6.0.3, release, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	13m 32s
Linux (swift:6.1.2, debug, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	1m 52s
Android (nightly-6.2, aarch64)	3m 53s
macOS (debug)	1m 44s
Linux (swift:6.0.3, release)	14m 4s
Linux (swift:6.0.3, debug, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	1m 58s
Linux (swift:6.1.2, release, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	12m 45s
Android (6.1, aarch64)	4m 46s
	1h 39m 16s

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