Add budget-aware Vulkan memory policies

[antono3]

Summary

• add deterministic, explainable memory-type policies for GPU-only, upload, readback, and automatic usage
• add optional VK_EXT_memory_budget discovery, refresh, strict/preferred budget behavior, and heap diagnostics
• retry allocations after cached-block reclamation and fall through to compatible memory types on allocation pressure
• add non-coherent flush/invalidate helpers aligned to nonCoherentAtomSize
• add policy-based buffer, image, raw-allocation, and upload-ring APIs while preserving every existing MemType API
• document the higher-level policy/planning/Vulkan-ownership model and the conservative dedicated-image rule
• pin the authoritative CI compiler to V 0.5.2 and add ASan/UBSan coverage

Compatibility

Existing allocate, create_buffer, create_dedicated_buffer, create_image, and new_upload_ring behavior remains available. The new API is additive. antono2.memory remains the small CPU-only planning layer; Vulkan-specific policy stays in this repository.

Validation

• v fmt -verify .
• v vet block_pool.v block_pool_test.v mapped_memory.v mapped_memory_test.v memory_policy.v memory_policy_test.v upload_ring.v upload_ring_test.v vulkan_memory_allocator.v vulkan_memory_allocator_test.v
• v test . (5/5)
• full ASan/UBSan suite with the exact V 0.5.2 release (5/5)
• real lavapipe example: shared upload-buffer suballocation, simultaneous mapping, policy-selected dedicated image, reported live heap budget, policy-selected upload ring, slice flushing, wraparound, retirement, and cleanup