Adopt memory v1.5 and demonstrate fenced upload retirement

[antono3]

The buffer-suballocation example now holds upload slices in a bounded retirement queue until actual Vulkan fence completion. It exercises queue backpressure and ring wraparound, then verifies copied values through mapped host readback before cleanup.

Pin antono2.memory@v1.5.0 in both dependency manifests and prepare allocator v2.7.0. The existing UploadRing API is preserved. The guide uses configured dependencies and compiler/driver environment variables rather than a developer-specific checkout layout.

Validation:

• Real fenced-copy/readback checks passed with validation enabled on Lavapipe and NVIDIA hardware using released V 0.5.2.
• The same example passed with pinned current V and explicit V3 on Lavapipe.
• Dependency-manifest, allocator and platform CI checks are required before merge.

The example reports completion from one ordered queue; unrelated queues need separate completion domains or explicit aggregation.