Bug Fix: Added missing constant term contribution in energy_expectation

[ezerc]

Description

The energy_expectation() function in utilities.oy did not account for constant terms, and the respective test wasa ring of disagrees Hamiltonian with vanishing constant.

I have fixed the issue by adding the constant after the averaging, I have modified the current test by adding a constant term to the ring of disagrees Hamiltonian and added a second test on a Minimum Vertex Cover Hamiltonian.

Checklist

• [x] I have performed a self-review of my code.
• [x] I have commented my code and used numpy-style docstrings
• [x] I have made corresponding updates to the documentation.
• [x] My changes generate no new warnings
• [x] I have added/updated tests to make sure bugfix/feature works.
• [x] New and existing unit tests pass locally with my changes.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Modified test_utilities.py as per in the description

[codecov[bot]]

Codecov Report

Merging #197 (9d39cb1) into dev (1fe7e02) will increase coverage by 0.02%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #197      +/-   ##
==========================================
+ Coverage   88.76%   88.79%   +0.02%     
==========================================
  Files          32       32              
  Lines        5786     5799      +13     
==========================================
+ Hits         5136     5149      +13     
  Misses        650      650              

Impacted Files	Coverage Δ
tests/test_utilities.py	99.42% <100.00%> (+0.02%)	:arrow_up:

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[Q-lds]

@vishal-ph, I leave you the honour of merging. My only question is whether we could have more tests ... but I couldn't think of any