Default IM3D_MALLOC/IM3D_FREE macros should be defined in `im3d.h` about im3d HOT 6 CLOSED

bool Im3d_ImplDX12_Init(ID3D12Device* device, int num_frames_in_flight, DXGI_FORMAT rtv_format, ID3D12DescriptorHeap* heap)
{
    Im3d::AppData& ad = Im3d::GetAppData();
    IM3D_ASSERT(ad.m_rendererData == nullptr && "The im3d already initialized at platform backend!");
    //  IM3D_ASSERT(device);
    //  IM3D_ASSERT(num_frames_in_flight > 0);
    //  IM3D_ASSERT(heap);

    Im3d_ImplDX12_Data* data = (Im3d_ImplDX12_Data*)IM3D_MALLOC(sizeof(Im3d_ImplDX12_Data));
    ad.m_rendererData = (void*)data;

    data->device_ = device;
    data->heap_ = heap;
    data->num_frames_in_flight_ = num_frames_in_flight;
    data->frame_index_ = UINT_MAX;
    data->rtv_format_ = rtv_format;
    data->frame_resources_ = (Im3d_ImplDX12_RenderBuffers*)IM3D_MALLOC(num_frames_in_flight * sizeof(Im3d_ImplDX12_RenderBuffers));
        
    for (int index = 0; index < num_frames_in_flight; ++index)
    {
        Im3d_ImplDX12_RenderBuffers* render_buffer = &data->frame_resources_[index];

        render_buffer->index_buffer_ = nullptr;
        render_buffer->vertex_buffer_ = nullptr;
        render_buffer->index_buffer_size_ = 0;
        render_buffer->vertex_buffer_size_ = 0;
    }

	(...)

    return true;
}