[antono3]

Summary

Use concrete null struct-pointer types for budget-extension and example queue-family enumeration. This avoids the V3 null-dereference bug reported with a dependency-free reproducer in vlang/v#31480. No public API, allocator policy, dependency pin or release metadata changes.

Verification

• Eight allocator V test files pass with current V3 f7afd8eadc74d7937eaa8938305bab3195bdc8df and TinyCC.
• All eight test files also pass with supported stable V/TinyCC.
• Current V3 hardware video playback progresses past supports_memory_budget after this fix (it crashes there before the fix).
• Separate full buffer-suballocation example diagnostics are ongoing and are not claimed as passing here.