Move the pick buffer out of `PickVolume`

## Use Case

Currently, `PickVolume` owns the pick buffer, which means that all pick rendering needs to be handled by it, including for other meshes.

Ideally, `ThreeJsPanel` should own the pick buffer instead.

## Solution

- [ ] Remove the pick buffer from `PickVolume` and move it into `ThreeJsPanel` instead.
- [ ] Pass the pick buffer into the animate functions so `PickVolume` can write to it.
- [ ] Optional (possible second PR): refactor existing mesh shaders so they can write to the pick buffer in the same render pass?

## Alternatives

_Please describe any alternatives you've considered, even if you've dismissed them_