Add SLATE dense LU solver wrapper

[AJ0070]

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

• Added SLATEFactorization for dense LU solves.
• Added support for real, complex, and multiple right-hand sides.
• Added lazy SLATE library loading and slate_isavailable().
• Added documentation and guarded tests.

The wrapper dynamically loads libslate_lapack_api and calls its LAPACK-compatible slate_*gesv functions.

It supports Float32, Float64, ComplexF32, and ComplexF64. Other real and complex element types are promoted where necessary.

fixes #54
AI Disclosure: Used GPT 5.4

[AJ0070]

@ChrisRackauckas

[ChrisRackauckas]

This should get a JLL?

[AJ0070]

I have made a PR for it but I think it will take some time to get merged. I have started looking into #143 and will soon start making PRs for it.