Doc: Prettify petab.select docs

[dweindl]

Fix return type documentation, cross references, typo, deprecated type annotations.

[codecov-commenter]

Codecov Report

Attention: 384 lines in your changes are missing coverage. Please review.

Comparison is base (160c2a8) 88.16% compared to head (7f40c2b) 82.48%.
Report is 475 commits behind head on develop.

Files	Patch %	Lines
pypesto/ensemble/ensemble.py	69.77%	68 Missing ⚠️
...ypesto/hierarchical/spline_approximation/solver.py	82.62%	53 Missing ⚠️
pypesto/ensemble/util.py	65.13%	38 Missing ⚠️
pypesto/hierarchical/optimal_scaling/solver.py	93.53%	26 Missing ⚠️
pypesto/history/base.py	88.57%	24 Missing ⚠️
pypesto/hierarchical/petab.py	84.76%	23 Missing ⚠️
pypesto/engine/mpi_pool.py	0.00%	22 Missing ⚠️
pypesto/hierarchical/inner_calculator_collector.py	88.51%	17 Missing ⚠️
...pesto/hierarchical/spline_approximation/problem.py	89.18%	16 Missing ⚠️
pypesto/hierarchical/problem.py	89.05%	15 Missing ⚠️
... and 15 more

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Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1255      +/-   ##
===========================================
- Coverage    88.16%   82.48%   -5.69%     
===========================================
  Files           79      148      +69     
  Lines         5257    12066    +6809     
===========================================
+ Hits          4635     9953    +5318     
- Misses         622     2113    +1491     

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[dilpath]

Looks good, thanks!