Pick buffer is noisy when orthogonal to volume Z axis

## Description

Noticeable when the view axis is orthogonal to the Z-axis. The contour shader directly samples from the pick buffer, so the noise is coming from the pick buffer itself.

## Expected Behavior

- The outline should be smooth.

## Reproduction

In `public/index.ts`, add the following lines after `loadTestData()` is called on L1512:
```
view3D.setCameraState({
position: [-0.612766, -0.1718693, 0],
target: [-0.013957, -0.0330511, 0],
});

setTimeout(() => {
view3D.setSelectedID(myState.volume, myState.colorizeChannel, 103);
}, 1000);
setTimeout(() => {
view3D.setSelectedID(myState.volume, myState.colorizeChannel, 103);
}, 1500);
```

## Environment

Windows 11, Chrome