Pure python rewrite

[tlambert03]

Here's the big one!

This PR would thank @funkey's C++ code for its service and move to a pure python interface where we dispatch to gurobipy or PySCIPOpt for the backend implementations (both of which are available on pypi and conda!).

This makes ilpy (and therefore motile) dramatically easier to distribute, even just with pypi (no conda needed at all). End users can pip install gurobipy or conda install -c gurobipy if they have a license and want to bring it in.

all tests are currently passing locally with essentially no changes to the test suite. So i think the public API should be essentially untouched.

cc @cmalinmayor, @funkey

closes #68
closes #69

[codecov]

Codecov Report

Attention: Patch coverage is 79.13669% with 87 lines in your changes missing coverage. Please review.

Project coverage is 85.06%. Comparing base (0fdfae7) to head (88202a6).
Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ilpy/solver_backends/_gurobi.py	34.28%	46 Missing ⚠️
src/ilpy/_components.py	84.67%	19 Missing ⚠️
src/ilpy/solver_backends/_scip.py	81.92%	15 Missing ⚠️
src/ilpy/_solver.py	90.90%	5 Missing ⚠️
src/ilpy/__init__.py	95.00%	1 Missing ⚠️
src/ilpy/solver_backends/__init__.py	96.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #70      +/-   ##
==========================================
+ Coverage   75.72%   85.06%   +9.34%     
==========================================
  Files          17       10       -7     
  Lines         828      663     -165     
  Branches      154        0     -154     
==========================================
- Hits          627      564      -63     
+ Misses        136       99      -37     
+ Partials       65        0      -65     

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[tlambert03]

still need to reimplement callbacks