Rely on LinearAlgebra.eigsort! for sorting eigenvalues of the

[andreasnoack]

symmetric solver

Some profiling revealed that the sorting used until this PR had significant overhead for smaller and medium sized problems. In addition, the values would be sorted twice if the user supplied a non-standard sorting function.

As an example

Current master

julia> @btime GenericLinearAlgebra._eigen!(S) setup = (S = LinearAlgebra.SymTridiagonal(ones(100), 0.2*ones(99)));
  153.222 μs (12 allocations: 159.12 KiB)

This PR

julia> @btime GenericLinearAlgebra._eigen!(S) setup = (S = LinearAlgebra.SymTridiagonal(ones(100), 0.2*ones(99)));
  45.367 μs (3 allocations: 78.57 KiB)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.72%. Comparing base (bebae94) to head (ec8c7a3).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #151      +/-   ##
==========================================
- Coverage   91.80%   91.72%   -0.08%     
==========================================
  Files          10       10              
  Lines        1549     1547       -2     
==========================================
- Hits         1422     1419       -3     
- Misses        127      128       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.