fix: update code for wgpu 29.0.0 API changes

[Claude]

Fixes compilation failures after wgpu 28.0.0 → 29.0.0 upgrade due to breaking API changes.

Changes

• Pipeline layouts: bind_group_layouts now requires &[Option<&BindGroupLayout>] instead of &[&BindGroupLayout]

  • Updated lighting_shadows.rs to wrap bind group layout references with Some()

• Buffer mapping: BufferViewMut no longer provides direct iteration - use copy_from_slice() instead

  • Updated buffer_integration_test.rs to use the new API

// Before (wgpu 28.0.0)
bind_group_layouts: &[
    &camera_bind_group_layout,
    &light_bind_group_layout,
]

// After (wgpu 29.0.0)
bind_group_layouts: &[
    Some(&camera_bind_group_layout),
    Some(&light_bind_group_layout),
]

// Before (wgpu 28.0.0)
let mut view = buffer.get_mapped_range_mut();
for (i, byte) in view.iter_mut().enumerate() {
    *byte = i as u8;
}

// After (wgpu 29.0.0)
let mut view = buffer.get_mapped_range_mut();
let data: Vec<u8> = (0..256).map(|i| i as u8).collect();
view.copy_from_slice(&data);