Add threading APIs. Disable external LAPACK forwarding option.

[ViralBShah]

Add the get/set threading API that is available in macOS 15 onwards.

The LAPACK forwarding option in the API would not work without a dependency on LAPACK_jll etc. Best to let the user use their own LAPACK. This package just focusses on forwarding to Accelerate BLAS and LAPACK.

[codecov]

Codecov Report

❌ Patch coverage is 74.19355% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.22%. Comparing base (a89e716) to head (c98e77f).
⚠️ Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
src/AppleAccelerate.jl	74.19%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #88      +/-   ##
==========================================
+ Coverage   75.61%   76.22%   +0.60%     
==========================================
  Files           4        4              
  Lines         242      265      +23     
==========================================
+ Hits          183      202      +19     
- Misses         59       63       +4     

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