use f string

[Christian-B]

part of SpiNNakerManchester/SupportScripts#100

see https://docs.astral.sh/ruff/rules/printf-string-formatting/

testing shows that

• f"{an_int}" works the same as "%d" % an_int

  • And the fsrting is better if an_int is actually a float

• f"{a_float} works the same as "%g" % a_float

-a string can be both an f and an r string

• leaving the variable a t would work but I changed it to ms to avoid confusion.