polars-ds: Add version 0.12.1

[luhenry]

• Package: polars-ds
• Version: 0.12.1
• Source: https://github.com/abstractqqq/polars_ds_extension
• Docs: https://pypi.org/project/polars-ds/

Compiles polars_ds, a PyO3/maturin Rust plugin adding statistics, ML metrics and feature-engineering expressions to the Polars dataframe library. Upstream publishes no riscv64 wheel.

Mirrors the build-wheels job of upstream's CI.yml.

Differs from upstream

• Builds one cp39-abi3 wheel for riscv64; upstream's own matrix never targets riscv64 at all
• Overrides the fat-LTO release profile to codegen-units=16/opt-level=1, like polars-runtime does for py-polars itself
• Drops upstream's x86-64 CPU-feature-tuned RUSTFLAGS; not applicable to riscv64

Matrix: single cp39-abi3 (pyo3 carries abi3-py39 unconditionally)

Testing

• Runs one of the README's documented expressions (query_roc_auc/query_log_loss) against the published polars wheel, instead of upstream's numpy/great-tables-dependent pytest suite

License: OK

Built on cp39 (abi3); CI pending.