Support input data on log scale

[hillalex]

Allow user to pass data on a log scale. If the scale=log argument is passed to the model, don't transform the data before/after model fitting.

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.48%. Comparing base (bc4da25) to head (3fe300a).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
R/biokinetics.R	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #19      +/-   ##
==========================================
- Coverage   92.60%   92.48%   -0.12%     
==========================================
  Files           8        8              
  Lines         419      426       +7     
==========================================
+ Hits          388      394       +6     
- Misses         31       32       +1     

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