f-string formatting
Hello @lhoestq, ```make style``` is applied as asked. :)
**Fix #3257**

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

Modules in **_src/Datasets/_**: 
- [x] **commands**
- [x] **features**
- [x] **formatting**
- [x] **io**
- [x] **tasks**
- [x] **utils**


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

-A correction of the first PR (#3267)-
