fix energy statistic bug

[sampan501]

Reference issue

Closes #341

Type of change

Bug

What does this implement/fix?

Fixed Energy stat bug, adds unit test based on issue.

Additional information

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (ace5d06) 96.72% compared to head (284d13a) 96.73%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #368   +/-   ##
=======================================
  Coverage   96.72%   96.73%           
=======================================
  Files          86       86           
  Lines        3853     3859    +6     
=======================================
+ Hits         3727     3733    +6     
  Misses        126      126           

Impacted Files	Coverage Δ
hyppo/ksample/energy.py	100.00% <100.00%> (ø)
hyppo/ksample/tests/test_energy.py	100.00% <100.00%> (ø)

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