fix(wireframes): only set depth bias when topology is triangles

[kfc35]

Objective

• Fixes 3d_shapes example is broken #23772
• Fixes 2d_shapes example rendering error #23774
• Fixes wireframe plugins. wgpu added some validation around DepthBiasState:

            if (ds.bias.is_enabled() || ds.bias.clamp != 0.0)
                && !desc.primitive.topology.is_triangles()
            {
                return Err(pipeline::CreateRenderPipelineError::DepthStencilState(
                    pipeline::DepthStencilStateError::DepthBiasWithIncompatibleTopology(
                        desc.primitive.topology,
                    ),
                ));
            }

ds.bias.is_enabled() returns true if either constant and slope_scale are non zero values.
This was causing the following error message when running the 2d_shapes and 3d_shapes examples (the following msg is for 3d_shapes)

2026-04-13T05:14:12.638678Z ERROR bevy_render::error_handler: Caught rendering error: Validation Error

Caused by:
  In Device::create_render_pipeline, label = 'wireframe_3d_pipeline'
    Depth/stencil state is invalid
      Depth bias is not compatible with non-triangle topology LineList

Solution

• Wireframe plugins should only set the depth bias’ slope_scale to a non-zero value if the topology is triangles. This complies with the validation done in wgpu.

Testing

• I can now turn on the wireframes in cargo run --example 2d_shapes and cargo run --example 3d_shapes

[atlv24]

Thank you!