Drop Python 3.9 support

[matthewdouglas]

Removes support for Python 3.9.

Additionally, Ruff is upgraded and fixes made as appropriate.

Resolves #1777

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[albertvillanova]

@matthewdouglas, have you tested on Python 3.14? We are getting this error on trl: huggingface/trl#4225 (comment)

    import bitsandbytes as bnb
.venv/lib/python3.14/site-packages/bitsandbytes/__init__.py:19: in <module>
    from .backends.default import ops as default_ops
.venv/lib/python3.14/site-packages/bitsandbytes/backends/default/ops.py:324: in <module>
    @torch.compile
     ^^^^^^^^^^^^^
.venv/lib/python3.14/site-packages/torch/__init__.py:2590: in compile
    raise RuntimeError("torch.compile is not supported on Python 3.14+")
E   RuntimeError: torch.compile is not supported on Python 3.14+

[matthewdouglas]

@albertvillanova Thanks for pointing that out. I think it's likely to work with torch nightly, but haven't tested it on the main releases. We probably need to better guard our use of the @torch.compile decorator. Will add that to our backlog.

bitsandbytes 0.47.0 may actually work with Python 3.14 for the time being, as it doesn't have this use of torch.compile in it.

[albertvillanova]

Thanks for the quick follow-up and the additional context. 🤗

We'll keep an eye on the progress regarding the @torch.compile guarding and the compatibility updates. We'll also test with bitsandbytes 0.47.0 once released as suggested.

[matthewdouglas]

@albertvillanova bitsandbytes==0.47.0 is a past existing release that can be used today (current is 0.48.2). Since we didn't have that usage of torch.compile I would expect it to just work, but it would be broken in 0.48+.

I'm planning to get a v0.49.0 release out by end of year, and will create a new issue for this and make sure to include it.

[matthewdouglas]

#1813

[matthewdouglas]

@albertvillanova #1831 should fix this!