Set __all__

[dweindl]

1. Avoids littering the namespace on star imports more than necessary
2. Simplifies cross-references to documentation, e.g., in addition to petab_select.problem.Problem, we can also now reference petab_select.Problem. This wasn't possible before.
3. Now also https://petab-select--72.org.readthedocs.build/en/72/generated/petab_select.html is populated. (To be decided whether we want to have only the top-level imports or only the individual modules.)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7c71053) 60.61% compared to head (082b254) 60.92%.
Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #72      +/-   ##
===========================================
+ Coverage    60.61%   60.92%   +0.30%     
===========================================
  Files           14       14              
  Lines         1521     1533      +12     
===========================================
+ Hits           922      934      +12     
  Misses         599      599              

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[dilpath]

Looks good. Many methods aren't expected to be used by users directly (e.g. in misc.py), but fine to doc them anyway

[dweindl]

Many methods aren't expected to be used by users directly

Agreed. Feel free to remove those, I didn't want break anything already using petab_select. Merge at your convenience.

e.g. in misc.py

There is petab_select/__init__.py:from .misc import *, that should then probably be removed.