Replacing .format() and % by f-strings
**Fix #3257**

Replaced _.format()_ and _%_ by f-strings in the following modules : 
- [x] **tests**
- [x] **metrics**
- [x] **benchmarks**
- [x] **utils**
- [x] **templates**

Will follow in the next PR the modules left : 
- [ ] **src**

Module **datasets** will not be edited as asked by @mariosasko 

PS : black and isort applied to files
