Make BosonBath align with QuTiP-BoFiN

[ytdHuang]

as title

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.85%. Comparing base (56d28c4) to head (a0d9b40).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #127      +/-   ##
==========================================
- Coverage   91.67%   89.85%   -1.83%     
==========================================
  Files          24       24              
  Lines        1478     1478              
==========================================
- Hits         1355     1328      -27     
- Misses        123      150      +27     

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