Add `.delete_constraints` method because repeated constraint deletion is slow

[staadecker]

Hi Yue,

I hope you're doing well!

I've received reports that repeatedly deleting linear constraints in Gurobi (via the .delete_constraint method) is so slow that often it is faster to simply re-create the model from scratch. This is particularly an issue for iterative optimization problems where users may want to modify and/or delete constraints on each iteration without recreating the model from scratch.

Looking at PyOptInterface's code, it does seem that each repeated call to .delete_constraint triggers both:

1. An expensive re-indexing (via GurobiModel::delete_constraint -> GurobiModel::_constraint_index -> ChunkedBitVector::get_index -> ChunkedBitVector::update_to)
2. A Gurobi update (via GurobiModel::delete_constraint -> GurobiModel::_constraint_index -> GurobiModel::_update_for_constraint_index -> GurobiModel::update -> gurobi::GRBupdatemodel)

Would you be open to adding a delete_constraints method similar to delete_variables? I expect such a method could be much much more efficient given that Gurobi supports deleting multiple constraints at once and your ChunkedBitVector can delete multiple indexes lazily (very neat btw!).

Cheers,
Martin