Add Support for Sparse Matrices in quadform()

[RoyiAvital]

Add support for SparseMatrixCSC in quadform().
Fixes #725 .

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.20%. Comparing base (6daf81c) to head (9235307).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #726      +/-   ##
==========================================
- Coverage   98.25%   98.20%   -0.05%     
==========================================
  Files          88       88              
  Lines        5203     5121      -82     
==========================================
- Hits         5112     5029      -83     
- Misses         91       92       +1     

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[RoyiAvital]

I think there is no Sparse Problem or they are converted into dense matrices.
This is the reason the sparse path is not covered.

[odow]

I think there is no Sparse Problem or they are converted into dense matrices. This is the reason the sparse path is not covered.

Yeah we need to add some new tests.

[RoyiAvital]

I can formulate a problem.
Yet I am not sure where should I stick it and how.
Maybe the simplest path would be just wrap one existing one with sparse()?

[odow]

It's just tooooo easy to make mistakes without tests. I swear when I write code without tests the probability that there is a bug is >99%.

[RoyiAvital]

Could it be that the test has a bug :-)? I don't understand where A is missing.

[odow]

Oops. I copy pasted from my local and didn’t get it all haha. See what I mean 😄