Port JAX LAPACK custom calls to XLA's FFI (API v4)
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Port JAX LAPACK custom calls to XLA's FFI (API v4)

- Upgrade CPU custom calls to FFI.
- Fix the array shape bug in the Tridiagonal Reduction kernel (insufficient allocation, shape off by one).
- Correct and extend the `_lapack` module stub to not produce warnings.
- Make Schur Decomposition return a fixed number of values.
- (WiP) Update the implementation of Schur form to consider the `select` parameter.
