BufferPolylineCollection: Missing czm_pixelRatio handling

### What happened?

BufferPolylineCollection is missing czm_pixelRatio in VS, causing line.width to render inconsistently on high-DPI vs. low-DPI displays.

### Reproduction steps

Compare:

- https://github.com/CesiumGS/cesium/blob/0dfbb658266fd1a4f6961dc51a5d260de1a81cf8/packages/engine/Source/Shaders/BufferPointMaterialVS.glsl#L29-L30
- https://github.com/CesiumGS/cesium/blob/0dfbb658266fd1a4f6961dc51a5d260de1a81cf8/packages/engine/Source/Shaders/BufferPolylineMaterialVS.glsl

### Sandcastle example

_No response_

### Environment

n/a

### AI acknowledgment

- [ ] I used AI to generate this issue report.
- [ ] (If the above is checked) I have reviewed the AI-generated content before submitting.

Start by comparing packages/engine/Source/Shaders/BufferPolylineMaterialVS.glsl with BufferPointMaterialVS.glsl at the referenced lines, focusing on how pixel ratio is handled. Verify the polyline shader applies the equivalent handling so line.width renders consistently on high-DPI and low-DPI displays.

Written by the indexing model from the issue text.