Add support for PEP701

[parona-source]

• fstrings are broken into several distinct tokens in py3.12, reattach
  them together as a singular string to preserve previous behavior.

Closes: #646

• Add unit tests and integration tests where applicable.
  If you've added an error code or changed an error code behavior,
  you should probably add or change a test case file under tests/test_cases/ and add
  it to the list under tests/test_definitions.py.
  If you've added or changed a command line option,
  you should probably add or change a test in tests/test_integration.py.
• Add a line to the release notes (docs/release_notes.rst) under "Current Development Version".
  Make sure to include the PR number after you open and get one.

[parona-source]

python3.12 -m tokenize <(echo 'f"""Do something. {f"This is a nested fstring."}"""')
0,0-0,0:            ENCODING       'utf-8'        
1,0-1,4:            FSTRING_START  'f"""'         
1,4-1,18:           FSTRING_MIDDLE 'Do something. '
1,18-1,19:          OP             '{'            
1,19-1,21:          FSTRING_START  'f"'           
1,21-1,46:          FSTRING_MIDDLE 'This is a nested fstring.'
1,46-1,47:          FSTRING_END    '"'            
1,47-1,48:          OP             '}'            
1,48-1,51:          FSTRING_END    '"""'          
1,51-1,52:          NEWLINE        '\n'           
2,0-2,0:            ENDMARKER      ''  
python3.11 -m tokenize <(echo 'f"""Do something. {f"This is a nested fstring."}"""')
0,0-0,0:            ENCODING       'utf-8'        
1,0-1,51:           STRING         'f"""Do something. {f"This is a nested fstring."}"""'
1,51-1,52:          NEWLINE        '\n'           
2,0-2,0:            ENDMARKER      ''