Skip eigenvector calculation when only eigenvalues are requested

[SolidTux]

This disables the eigenvector calculation when only eigenvalues are requested. From my tests this yields the same results and is much faster. (See also #255)

[codecov[bot]]

Codecov Report

Merging #256 (b38e324) into master (a561e5a) will decrease coverage by 1.98%. The diff coverage is 26.71%.

:exclamation: Current head b38e324 differs from pull request most recent head c551315. Consider uploading reports for the commit c551315 to get more accurate results

@@            Coverage Diff             @@
##           master     #256      +/-   ##
==========================================
- Coverage   89.01%   87.02%   -1.99%     
==========================================
  Files          71       71              
  Lines        3577     3707     +130     
==========================================
+ Hits         3184     3226      +42     
- Misses        393      481      +88     

Impacted Files	Coverage Δ
lax/src/eigh.rs	51.00% <0.00%> (-43.24%)	:arrow_down:
lax/src/lib.rs	54.16% <0.00%> (-45.84%)	:arrow_down:
ndarray-linalg/src/eigh.rs	50.54% <4.87%> (-41.29%)	:arrow_down:
ndarray-linalg/src/eig.rs	100.00% <100.00%> (+33.33%)	:arrow_up:
ndarray-linalg/src/solve.rs	72.65% <100.00%> (+0.07%)	:arrow_up:
ndarray-linalg/src/solveh.rs	73.26% <100.00%> (-0.48%)	:arrow_down:
ndarray-linalg/tests/eig.rs	100.00% <100.00%> (ø)
ndarray-linalg/tests/eigh.rs	100.00% <100.00%> (ø)
ndarray-linalg/tests/cholesky.rs	95.91% <0.00%> (-4.09%)	:arrow_down:
... and 20 more

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[termoshtt]

Sorry for long my absence. I drop this PR from 0.14.0 release because this is not necessary change.

[SolidTux]

Any updates? Anything you need from my side?