[Storage] Addressing Swift 6 issues with `Storage`'s instance management #5539

Job	Run time
pod-lib-lint (ios, macos-14)	3m 48s
quickstart (swift, macos-14, Xcode_15.3)	3m 24s
quickstart-ftl-cron-only	0s
pod-lib-lint (ios, macos-13)	4m 35s
pod-lib-lint (tvos, macos-14)	3m 9s
pod-lib-lint (tvos, macos-13)	4m 39s
pod-lib-lint (macos, macos-14)	4m 37s
spm (iOS, macos-13)	5m 50s
storage-integration-tests (Swift)	29m 0s
spm (iOS, macos-14)	5m 39s
pod-lib-lint (macos, macos-13)	4m 36s
storage-integration-tests (ObjC)	8m 31s
spm (tvOS, macos-13)	6m 59s
pod-lib-lint (watchos, macos-14)	3m 47s
spm (tvOS, macos-14)	5m 54s
pod-lib-lint (watchos, macos-13)	4m 18s
spm (macOS, macos-13)	6m 16s
spm (macOS, macos-14)	5m 26s
spm (catalyst, macos-13)	6m 48s
spm (catalyst, macos-14)	5m 44s
spm (watchOS, macos-13)	6m 42s
spm (watchOS, macos-14)	7m 35s
spm (macos-14, visionOS, Xcode_15.3)	10m 51s
storage-cron-only	0s
	2h 28m 8s

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