Enable pickling of Solver and SolverPtr

[dweindl]

Enable pickling of Solver and SolverPtr. For now, only with limited functionality and through storing solver settings in HDF5 files.

Related to #1126.

[codecov]

Codecov Report

❌ Patch coverage is 9.09091% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.79%. Comparing base (9ccd079) to head (e58d899).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
python/sdist/amici/swig_wrappers.py	11.11%	8 Missing ⚠️
include/amici/solver_cvodes.h	0.00%	1 Missing ⚠️
include/amici/solver_idas.h	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2987      +/-   ##
==========================================
- Coverage   76.52%   75.79%   -0.73%     
==========================================
  Files         308      308              
  Lines       19529    19540      +11     
  Branches     1499     1500       +1     
==========================================
- Hits        14944    14810     -134     
- Misses       4572     4717     +145     
  Partials       13       13              

Flag	Coverage Δ
cpp	72.89% <9.09%> (-0.04%)	⬇️
cpp_python	38.26% <9.09%> (-0.02%)	⬇️
petab	38.86% <9.09%> (-0.03%)	⬇️
python	69.62% <9.09%> (-0.04%)	⬇️
sbmlsuite-jax	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
include/amici/solver.h	100.00% <ø> (ø)
include/amici/solver_cvodes.h	50.00% <0.00%> (-50.00%)	⬇️
include/amici/solver_idas.h	50.00% <0.00%> (-50.00%)	⬇️
python/sdist/amici/swig_wrappers.py	91.96% <11.11%> (-7.07%)	⬇️

... and 6 files with indirect coverage changes

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