Remove constraints [wip]

[tlambert03]

this is a start on a removeConstraint method.

• It's currently implemented for the SCIP backend, but not gurobi.
• it works, however, if I add an unsatisfiable constraint and try to solve before removing the incompatible constraint, it leaves the solver unable to recover, even if I later make it satisfiable again.

(these lines are shown during the failed solve)

[scip_prob.c:2883] ERROR: invalid SCIP stage <10>
[ScipBackend.cpp:315] ERROR: Error <-8> in function call
[scip_prob.c:2883] ERROR: invalid SCIP stage <10>
[ScipBackend.cpp:315] ERROR: Error <-8> in function call
[scip_cons.c:1148] ERROR: cannot release last use of original constraint while an associated transformed constraint exists
[ScipBackend.cpp:317] ERROR: Error <-8> in function call
[scip_prob.c:2883] ERROR: invalid SCIP stage <10>
[ScipBackend.cpp:315] ERROR: Error <-8> in function call

[tlambert03]

sorry about the auto-formatting, will remove and reduce the diff

[codecov]

Codecov Report

Merging #46 (599ac42) into main (7fac186) will increase coverage by 16.58%.
The diff coverage is 87.50%.

@@             Coverage Diff             @@
##             main      #46       +/-   ##
===========================================
+ Coverage   75.72%   92.30%   +16.58%     
===========================================
  Files          17        4       -13     
  Lines         828      390      -438     
  Branches      154        0      -154     
===========================================
- Hits          627      360      -267     
+ Misses        136       30      -106     
+ Partials       65        0       -65     

Files	Coverage Δ
ilpy/wrapper.pyx	87.24% <87.50%> (-0.78%)	⬇️

... and 13 files with indirect coverage changes