Fix missing Lapack import for ndarray backends

[SauersML]

Summary

• add a cfg-gated ndarray_linalg::Lapack import so provider implementations compile when ndarray-linalg backends are enabled

Testing

• cargo test (fails: relies on Python-based reference checks that report low correlations without numpy/scipy/sklearn available in the container)
• cargo check --no-default-features --features backend_openblas (fails: OpenBLAS build script cannot download dependencies because TLS certificate verification fails in the environment)

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https://chatgpt.com/codex/tasks/task_e_68d35de1fdc8832eb12158f82190f32e