Fix tests and methods with AMD ROCM

[mlazzarin]

Closes #34.

• I fixed the rocblas_status_not_implemented issue by using NumPy instead of CuPy for eigh and eigvalsh.
  The changes apply only to CuPy with AMD GPUs.
• I completed the regression tests by running the tests on a machine with an AMD GPU and saving the output.

In order to close #34, we need also to merge qiboteam/qibo#501 in the Qibo repository.

[codecov]

Codecov Report

Merging #36 (33c7293) into backendcls (aa3a150) will not change coverage.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##           backendcls       #36   +/-   ##
============================================
  Coverage      100.00%   100.00%           
============================================
  Files               9         9           
  Lines             977       992   +15     
============================================
+ Hits              977       992   +15     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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Impacted Files	Coverage Δ
src/qibojit/custom_operators/backends.py	100.00% <ø> (ø)
src/qibojit/custom_operators/__init__.py	100.00% <100.00%> (ø)
src/qibojit/tests/test_backends.py	100.00% <100.00%> (ø)

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[stavros11]

Looks good to me.

One possibility to avoid the if self.engine.name == "cupy" and self.engine.is_hip checks would be to rename the current CupyBackend to CUDABackend and create a new HIPBackend that inherits it and re-implements the required methods that do not work for hip. This would require to define some new methods in the backends.AbstractBackend here. As discussed with @mlazzarin it would be better to first merge this to #35 to avoid having many open PRs and we could consider this refactoring later.

[scarrazza]

@mlazzarin thanks for this. Let's merge this now and keep the inheritance for a future PR.