Adds solvent floor and min halflife field for aerosol processes

[boulderdaze]

Adds solvent floor and min halflife field for aerosol processes to support MUSICA tutorial.
No tests were added because we aren't sure if this should be part of the user configuration yet.
Issue to track this has been created:

• Evaluate whether solvent_floor and min_halflife fields belong in the public API. #297

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.03%. Comparing base (7bf5f06) to head (0c52fc7).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #296   +/-   ##
=======================================
  Coverage   88.03%   88.03%           
=======================================
  Files          44       44           
  Lines        2474     2474           
=======================================
  Hits         2178     2178           
  Misses        296      296           

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[K20shores]

I would rather do this properly, adding tests, documentation, examples, since there are relatively few of these. If we find out we don't want to support them, we can always revert this PR