add isotopic ventilation ratio to physics (f_heavy to f_light)

[AgnieszkaZaba]

• populate notebook (it might be after a cleanup)

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.40%. Comparing base (2918dda) to head (82496dc).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...hysics/isotope_ventilation_ratio/brutsaert_1982.py	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1532      +/-   ##
==========================================
- Coverage   85.41%   85.40%   -0.01%     
==========================================
  Files         389      391       +2     
  Lines        9514     9526      +12     
==========================================
+ Hits         8126     8136      +10     
- Misses       1388     1390       +2     

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