[Vulkan][32-bit] non-dispatchable handles do not fit in void* on i586

Problem

The Vulkan backend does not compile on 32-bit x86/i586. In src/vt/vulkan/vulkan_context.cpp, it asserts that Vulkan handles fit in void*:

static_assert(sizeof(VkBuffer) <= sizeof(void*), "VkBuffer must fit in void*");
static_assert(sizeof(VkDeviceMemory) <= sizeof(void*), "VkDeviceMemory must fit in void*");

With the Vulkan headers on i586, the assertions fail because the comparison is 8 <= 4. Vulkan non-dispatchable handles such as VkBuffer and VkDeviceMemory are 64-bit values even when the host pointer size is 32-bit.

The backend then packs these handles through void* in Pack/Unpack, and the public backend context stores buffer and memory handles as void*, so simply removing the assertions would not be sufficient.

Reproducer

Build v0.0.2 on i586 with:

-DVLLM_CPP_VULKAN=ON

The build fails in src/vt/vulkan/vulkan_context.cpp with:

error: static assertion failed: VkBuffer must fit in void*
the comparison reduces to (8 <= 4)
error: static assertion failed: VkDeviceMemory must fit in void*
the comparison reduces to (8 <= 4)

Proposed direction

Use an architecture-independent opaque handle representation, such as a dedicated 64-bit storage type for non-dispatchable handles, and avoid packing them into void*. Dispatchable pointer handles can remain pointer-sized.

The openSUSE package currently disables the Vulkan backend on 32-bit x86 as a downstream workaround.

Start in src/vt/vulkan/vulkan_context.cpp by tracing the VkBuffer and VkDeviceMemory static assertions, then inspect the Pack/Unpack paths and the public backend context fields that store these handles. Build v0.0.2 with -DVLLM_CPP_VULKAN=ON on i586; done means the Vulkan backend compiles without routing non-dispatchable handles through void*.