Default learning rate for `register_volumewise` is bad

### ConfUSIus version

v0.4.0

### Python version

3.14

### Operating system

Linux

### Installation

using uv

### Description

The default `"auto"` learning rate is pretty bad for register_volumewise, since it tends to oscillate a lot and leads to creating a lot of motion in the final "corrected" recording. So we should probably set a conservative value of `0.01` instead of using auto-mode!