Bundled Biopython code: SyntaxWarning on Python 3.8+ and one module that cannot be compiled #11

Claude reports: compiling every .py file of the repository with Python 3.14 (after the escape-sequence fix, which is complete) leaves these problems in the bundled Bio code:

• Bio/Nexus/Nexus.py:918 state is ','
• Bio/KEGG/__init__.py:82 item is not ""
• Bio/Restriction/Restriction.py:2285, 2288, 2290 k is 'sequence' / 'rb' / 'linear'

Each prints SyntaxWarning: "is" with 'str' literal (seen in Sublime's console when Bio.Nexus is imported), and comparing strings with is only works by accident of interning. Use == / !=.

• Bio/PopGen/FDist/Async.py:91-92 uses self.async; async is a reserved word since Python 3.7, so the file is a SyntaxError and the module cannot be imported.

Tested on Sublime Text build 4215 (portable, Windows), plugin host Python 3.14, installed through the Package Control Install Package picker (BioPythonUtils 2017.12.18.15.00.45, which already contains the fixes for #3), then removed again. Line numbers are those of BioPythonUtils.py on master (de058c4).