feat(swift): support enum/time serialization for swift

[chaokunyang]

Why?

• Align Swift package/module naming with the rest of the project (ForySwift -> Fory) and simplify target layout.
• Add missing built-in xlang date/time support and macro-generated enum serialization support.
• Increase Swift test coverage for these features and for weak-reference tracking behavior.

What does this PR do?

• Renames Swift package products/targets and source directories:
  • ForySwift -> Fory
  • ForySwiftMacros -> ForyMacro
  • ForySwiftTests -> ForyTests
  • Moves xlang peer target to Tests/ForyXlangPeer
• Adds DateTimeSerializers.swift with:
  • ForyDate (.date)
  • ForyTimestamp (.timestamp, with second/nanos normalization)
  • Date: Serializer bridge using timestamp encoding
• Wires date/time support into deserialization paths (TypeResolver and FieldSkipper).
• Updates Context helper dispatch to call module-global read/write helpers instead of ForySwift.* symbols.
• Extends @ForyObject macro to support enums:
  • no-payload enums -> ordinal enum serialization (ForyTypeId.enumType)
  • associated-value enums -> tagged-union serialization (ForyTypeId.typedUnion)
• Simplifies ForyXlangPeer by replacing handwritten enum/date/union serializers with macro-based enums and shared ForyDate/ForyTimestamp types.
• Adds/updates tests:
  • DateTimeTests.swift for date/timestamp type IDs and round-trip behavior
  • EnumTests.swift for enum and tagged-union round trips
  • ForySwiftTests.swift coverage for weak self-reference tracking

Related issues

#1017
#3349

Does this PR introduce any user-facing change?

• Does this PR introduce any public API change?
• Does this PR introduce any binary protocol compatibility change?

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