Trivia: methods for molar and isotopic mixing ratio and molecular isotope ratio; new test for Mv

[AgnieszkaZaba]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.77%. Comparing base (c30b62d) to head (06e22a1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1782   +/-   ##
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  Coverage   86.76%   86.77%           
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  Files         414      414           
  Lines       10485    10500   +15     
=======================================
+ Hits         9097     9111   +14     
- Misses       1388     1389    +1     

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[AgnieszkaZaba]

Due to changes in Mv formula, eps constant is changed (https://github.com/open-atmos/PySDM/pull/1782/changes#diff-a92c92afb234b4c133efa00e86436fc4ba428e59cfa9ae1f7ce8d861e53e0951L807)
It might be connected to this issue #1207.
Hence, the error in Rozanski & Sonntag example(https://github.com/open-atmos/PySDM/actions/runs/20957304845/job/60251181084?pr=1782#step:4:692).

With new formula Mv is slightly smaller (Mv_new - Mv_old = -2.2829816474778664e-09).