Quick follow-up release with a handful of fixes and cleanups in our Variant and XPC service layers:

• python: Add support for casting to uint64 Variant.
• node: Stop accepting redundant uint64 Variant casts. Use BigInt when creating uint64 GVariant values.
• node: Plug a leak in the Variant cast logic’s error handling.
• xpc-service: Drop support for redundant casts.