offload: Make logging more compact
Use a format of
[subsurface XXX] SYMBOL DETAILS
where SYMBOL indicates the offloading status:
- 🗙 - no offload
- ▲ - offload above, with background
- △ - offload above, no background
- ▼ - offload below, with background
- ▽ - offload below, no background
Edited by Matthias Clasen