Xpress 9.9+ backward compatibility and other updates

[brunoficoxpress]

Restore Xpress 9.9+ API backward compatibility and fix deprecation warnings

Closes # (if applicable).

Changes proposed in this Pull Request

Xpress 9.8 renamed several API methods (e.g. loadproblem → loadLP/loadMIP/loadQP/loadMIQP, addnames → addNames, getDual → getDuals, etc.). PR #542 added try/except AttributeError wrappers to support both old and new API. These wrappers were inadvertently dropped in the Xpress direct-IO rewrite (787c4ce), reintroducing deprecation warnings when running against Xpress 9.9.

This PR restores the wrappers across all affected call sites in:

• Problem loading: selects loadLP, loadMIP, loadQP, or loadMIQP based on problem type (integer variables / quadratic objective); falls back to loadproblem on Xpress < 9.8
• Names: addNames() with addnames() fallback
• File I/O: readProb, readBasis, writeBasis, writeBinSol with lowercase fallbacks
• Solve helpers: postSolve, setLogFile with lowercase fallbacks
• Solution retrieval: getDuals() (was incorrectly getDual())

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[FabianHofmann]

wonderful! thanks for being so quick! In the refactoring I could not test newer xpress versions and according to the docs the loadproblem should still be valid, but this is better!

some of our projects still rely on xpress 9.4 which is the lower bound of the compat range. would you mind checking this version as well?

[FabianHofmann]

this is old xpress compatible?

[brunoficoxpress]

wonderful! thanks for being so quick! In the refactoring I could not test newer xpress versions and according to the docs the loadproblem should still be valid, but this is better!

some of our projects still rely on xpress 9.4 which is the lower bound of the compat range. would you mind checking this version as well?

Good points, thanks for the quick turnaround! Updated the PR with your suggestions.

Tested on both 9.4 and 9.6 - all LP/MIP tests pass on both versions, all pre-9.8 fallbacks exercised correctly (loadproblem, read, addnames, getDual, etc.).

If you get any issues, or some other queries related to Xpress, feel free to reach out or tag me. Thank you for the nice work with the library :).

[FabianHofmann]

What a responsiveness ;) thanks bruno, merging now