Add tests for the COO matvec method

[KyleVaughn]

Description:

The matvec method of the COO class will be tested for a combination of matrices and vectors with known results. Correct size of the output will also be tested.

Tasks:

Implement a test for COO matvec method which catches possible errors like

• [x] Incorrect output vector size

• [x] Incorrect multiplication operation

Definition of done:

Developing tests that test the accuracy of the matvec method

[Lazy-Beee]

I would suggest using the function interface virtual fp_type* matvec(fp_type* vecin) and I'll add this to the SparseMatrix class.

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Edit: change the api to avoid memory leak void matvec(fp_type* vecin, fp_type* vecout)

[KyleVaughn]

Review by @AnvayPradhan

[AnvayPradhan]

Would recommend multiple matrices and vectors with known outputs instead of just one to test with this matvec method

[sthvkbht]

Yes. That is the plan. Will make it more clear.