Convert formatting automatically to f-strings

Automatically convert formatting with the following call:
flynt -ll 2000 -v frappy*
Result: 303/381 auto-converted.
Failing conversions will be looked at manually in a follow-up commit.

Change-Id: Icd996b27221202faccc15af78e0380cf52ee37f2
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/30900
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Georg Brandl <g.brandl@fz-juelich.de>
Reviewed-by: Alexander Zaft <a.zaft@fz-juelich.de>

frappy_psi/ccu4.py

@@ -84,13 +84,13 @@ class HeLevel(HasIO, Readable):
         return self.query('hem')
 
     def write_empty_length(self, value):
-        return self.query('hem=%g' % value)
+        return self.query(f'hem={value:g}')
 
     def read_full_length(self):
         return self.query('hfu')
 
     def write_full_length(self, value):
-        return self.query('hfu=%g' % value)
+        return self.query(f'hfu={value:g}')
 
     def read_sample_rate(self):
         return self.query('hf')