Pass cross sectional area to `RCRWindkesselModel`

[LasNikas]

I noticed that it makes more sense to pass the cross sectional area instead of calculating it with the particle size. Also, it is not correct calculated in main, so this is actually a bug fix.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 89.60%. Comparing base (32679eb) to head (e0417cb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #992      +/-   ##
==========================================
- Coverage   89.60%   89.60%   -0.01%     
==========================================
  Files         120      120              
  Lines        8588     8587       -1     
==========================================
- Hits         7695     7694       -1     
  Misses        893      893              

Flag	Coverage Δ
total	89.60% <100.00%> (-0.01%)	:arrow_down:
unit	64.83% <100.00%> (-0.01%)	:arrow_down:

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