fix(iohandler): drop deprecated ast.Str and .s usage

[Barry-Lenhart]

What

IOHandler's function-call parsing (keep/iohandler/iohandler.py) checks literals with isinstance(arg, ast.Str) or isinstance(arg, ast.Constant) and reads arg.s.

Since Python 3.8 the parser emits ast.Constant for every literal, and ast.Str / .s are deprecated aliases:

• on Python 3.12 and 3.13 they emit DeprecationWarnings every time a templated function call is rendered,
• on Python 3.14 ast.Str is removed entirely, so this line would raise AttributeError.

The existing isinstance(..., ast.Constant) check already covers every case, so this uses it alone and reads .value (which .s was an alias for) in both places, for positional and keyword arguments.

Testing

On Python 3.12:

• pytest tests/test_iohandler.py: 68 passed, same as before.
• With -W error::DeprecationWarning:keep.iohandler.iohandler: 27 of the 68 tests fail on main and all 68 pass with this change.
• str(node.s) and str(node.value) give identical results for string, int, float, True and None literals.
• ruff check (the pinned 0.11.4) passes, and black suggests no changes to the touched lines.

I used an AI assistant (Claude) to help find this, make the change, and draft this description. I reviewed the change and ran the tests myself.

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[Barry-Lenhart]

Closing this, as I'm not able to sign the CLA at the moment. For anyone picking it up: the fix is just using the existing isinstance(..., ast.Constant) check on its own and reading .value instead of .s in keep/iohandler/iohandler.py (two places). ast.Str is removed in Python 3.14, and on 3.12 27 of the 68 tests in tests/test_iohandler.py fail with -W error::DeprecationWarning. Thanks!