Add support for time zones in `DateTag`. #224

Job	Run time
leaf-integration	3m 18s
unit-tests / api-breakage	1m 41s
unit-tests / linux-unit (swift:5.8-jammy)	1m 24s
unit-tests / linux-unit (swift:5.9-jammy)	1m 28s
unit-tests / linux-unit (swift:5.10-noble)	1m 37s
unit-tests / macos-unit (macos-13, ~15.2)	2m 15s
unit-tests / linux-unit (swiftlang/swift:nightly-6.0-jammy)	1m 49s
unit-tests / macos-unit (macos-14, latest-stable)	1m 17s
unit-tests / linux-unit (swiftlang/swift:nightly-main-jammy)	1m 56s
	16m 45s

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