Fix parameter scale in sample_from_prior

[dweindl]

Return sampled parameters on the parameter scale.
This broke in #329 & #335.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 74.00%. Comparing base (0e90fd9) to head (ab44d47).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
petab/v1/sampling.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #385   +/-   ##
========================================
  Coverage    74.00%   74.00%           
========================================
  Files           58       58           
  Lines         6470     6470           
  Branches      1115     1115           
========================================
  Hits          4788     4788           
  Misses        1260     1260           
  Partials       422      422           

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[PaulJonasJost]

Works for me!