SI units are not translatable

### What Happened?


The SI unit prefix and unit itself in the unit conversion plugin are not translatable in Weblate.

### Steps to Reproduce

1. Do ```killall io.elementary.wingpanel``` twice to fully kill the wingpanel
2. Run ```LANGUAGE=ja_JP.utf8 io.elemenatry.wingpanel```
3. Enter ```20m3->cm3``` in the search entry
4. See "meter" and "centimeter" are not translated ("meter cubed" should be "立方メートル" and "centimeter cubed" should be "立方センチメートル" in Japanese FYI)

### Expected Behavior

The SI unit prefix and unit itself in the unit conversion plugin should be also translatable in Weblate, and thus we can see it's translated in the plugin's UI too.

### OS Version

7.x (Early Access)

### Software Version

Latest release (I have run all updates)

### Log Output

_No response_

### Hardware Info

_No response_