v0.3.1

What's Changed

• [pre-commit.ci] pre-commit autoupdate by @pre-commit-ci in #191
• add COPT solver by @fneum in #190
• Retrieve solution before closing the gurobi env by @dannyopts in #193
• add MindOpt solver by @fneum in #188
• add MOSEK solver by @fneum in #189
• constant: ensure float value & improve printing of constants by @FabianHofmann in #194

Full Changelog: v0.3...v0.3.1