Fix nested f-string for Python <3.12

[schmidtwmark]

When I initially ran frames on my Mac with Python 3.8, I saw this error:

  File "/Users/markschmidt/.local/bin/frames", line 2708
    print(f"    {C.dim('Rotated:')} {r['source_dimensions']} {C.dim('→')} {r['dimensions']} {C.dim(f'({r["rotation"]})')}")
                                                                                                            ^
SyntaxError: f-string: unterminated string

This is because there are 3 layers of f-strings, the first using ", the second ', and the last using ". Repeated quotes weren't supported until Python 3.12

This makes sure that frames is compatible with Python 3.8, as described in the README.

Thanks for making an awesome tool!