Migrate to PyOptInterface

[staadecker]

Motivation 🎉

As discussed internally, this changes brings some important improvements:

• Out-of-the-box support for HiGHS open-source solver! Just use Model(solver="highs") and pip install highsbox
• ~2x faster since we avoid the slow .lp writing/parsing (based on the facility benchmarks)
• ~15% less lines of code while maintaining the functionality (deleted io.py, io_mappers.py, solvers.py, and user_defined.py !)
• Improved documentation!

Closes #57. Closes #75. Closes #60. Closes #19.

Thanks to @metab0t for the powerful PyOptInterface library, and the helpful responses!

Breaking changes ⚠️ ⚠️

Function	Change	Use instead
Model.to_file(file_path, use_var_names)	Renamed with changes	Model.write(file_path). Note: use_var_names should now be set when initializing the model.
Model.solve(solver, directory, use_var_names, log_fn, warmstart_fn, basis_fn, solution_file, log_to_console)	Renamed with changes	Model.optimize(). Note: parameters should be set through other means (e.g. model.attr.Silent = True instead of log_to_console=False)
Expression.value	Renamed	Expression.evaluate()
Config.print_float_precision	Renamed	Config.float_to_str_precision
Constraint.slack	Renamed	Constraint.attr.slack (Gurobi only)
Variable.RC	Renamed	Variable.attr.RC (Gurobi only)
Constraint.relax(...)	Changed behavior	Same as before except that it must be called before adding a constraint to the model.
Model.params (Gurobi only)	Changed behavior	Same as before except that if the parameter needs to be set during environment creation, instead use: Model(solver_env={"server_name":"bla"})
.to_str(...) and .to_str_table(...)	Changed signature	Parameters moved to pf.Config

Also:

• ⚠️ Gurobi must be installed through their website (not via pip) as we now use the Gurobi C API (not the Python API). Here is a way to automate this in a build environment. ⚠️
• Support for Python 3.8 is dropped.

Todo

• Remove old to_str code
• Fix failing tests
• Fix duals!
• Add documentation
• List breaking changes
• Testing of other solvers
• Fix map_elements warnings
• Test and support adding objective

[codecov]

Codecov Report

Attention: Patch coverage is 95.92593% with 11 lines in your changes missing coverage. Please review.

Project coverage is 95.71%. Comparing base (53c14ff) to head (d51e9b3).

Files with missing lines	Patch %	Lines
src/pyoframe/model.py	90.16%	6 Missing ⚠️
src/pyoframe/core.py	96.29%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #79      +/-   ##
==========================================
+ Coverage   94.61%   95.71%   +1.10%     
==========================================
  Files          13        9       -4     
  Lines        1448     1028     -420     
==========================================
- Hits         1370      984     -386     
+ Misses         78       44      -34     

Flag	Coverage Δ
smart-tests	95.71% <95.92%> (+1.10%)	⬆️

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[github-actions]

Lines Of Code

Language	Files	Lines	Code	Comments	Blanks	Complexity	Bytes
CSV	20 (+1)	292 (-977)	292 (-977)	0	0	0	3.2K (-9.5K)
Jupyter	2	2033	2033	0	0	0	62.4K (+3B)
License	1	21 (-2)	17 (-2)	0	4	0	1K (-72B)
Markdown	25	500 (+87)	327 (+68)	0	173 (+19)	0	18.2K (+2.8K)
Python	28 (-3)	4197 (-686)	3640 (-490)	212 (-81)	345 (-115)	184 (-19)	138.9K (-17.3K)
Solidity	5	217 (-980)	217 (-980)	0	0	2 (-2)	4.4K (-22.5K)
TOML	1	66 (+10)	60 (+10)	0	6	0	1.5K (+104B)
YAML	10 (+4)	720 (+495)	513 (+299)	153 (+150)	54 (+46)	0	21.9K (+16.2K)

[kjartan-at-bravos]

Just a minor comment on choice of method name. The code looks great and I am looking forward to testing it out!