Typed Matrix constructor and more stable tests

[jishnub]

I've removed the single-index getindex methods, as the AbstractArray fallback methods should suffice.

I've also ensured that the matrices are explicitly hermitian in the tests, which makes it less likely for cholesky to fail due to numerical precision issues. Further, I've added a random seed, which makes the tests easier to reproduce.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cd28425) 91.48% compared to head (c067537) 91.56%.

❗ Current head c067537 differs from pull request most recent head 5710a1b. Consider uploading reports for the commit 5710a1b to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #199      +/-   ##
==========================================
+ Coverage   91.48%   91.56%   +0.08%     
==========================================
  Files           9        9              
  Lines         681      676       -5     
==========================================
- Hits          623      619       -4     
+ Misses         58       57       -1     

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[devmotion]

Seems good to me, thank you!