Add Christiansen mapping for mapping christiansen bosons

[ddhawan11]

Context:
Add christiansen_mapping function

Description of the Change:
Added function for mapping hardcore bosonic operators to qubit operators using christiansen mapping

Benefits:

Possible Drawbacks:

Related GitHub Issues:

[sc-72640]

[austingmhuang]

I just took a look at some general stuff. Seems like the algorithm is not that complicated but I will double check tomorrow.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.65%. Comparing base (a672a9b) to head (b16e61c).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6623      +/-   ##
==========================================
+ Coverage   99.46%   99.65%   +0.18%     
==========================================
  Files         455      455              
  Lines       42784    42818      +34     
==========================================
+ Hits        42555    42669     +114     
+ Misses        229      149      -80     

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[soranjh]

Thanks @ddhawan11, looks good.