Add `lax::eigh::EighWork`, merge `lax::Eigh_` into `Lapack` trait

[termoshtt]

Same approach in #333 and #340

• Merge Eigh_ trait into Lapack trait
• Create new submodule eigh_generalized for generalized eigenvalue problem for symmetric/hermite matrices
• Add EighWork and EighGeneralizedWork

[codecov[bot]]

Codecov Report

Merging #341 (bef1083) into master (33e2dc3) will decrease coverage by 0.78%. The diff coverage is 68.87%.

@@            Coverage Diff             @@
##           master     #341      +/-   ##
==========================================
- Coverage   90.15%   89.37%   -0.79%     
==========================================
  Files          73       74       +1     
  Lines        4105     4217     +112     
==========================================
+ Hits         3701     3769      +68     
- Misses        404      448      +44     

Impacted Files	Coverage Δ
lax/src/eigh_generalized.rs	47.05% <47.05%> (ø)
lax/src/eigh.rs	97.53% <96.66%> (+2.53%)	:arrow_up:
lax/src/lib.rs	100.00% <100.00%> (ø)

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