`lp-polars` IO API writes different models to `lp` which are incorrect

[CharlieFModo]

Version Checks (indicate both or one)

• I have confirmed this bug exists on the lastest release of Linopy.

• I have confirmed this bug exists on the current master branch of Linopy.

Issue Description

When using io_api="lp-polars" the model file linopy writes is different to io_api="lp". These differences result in the models from lp-polars showing as infeasible on a commercial model I am working on. The issue seems to stem from constraints writing differently between the two APIs.

Reproducible Example

# N/A I have not reproduced the issue because I have encountered it on commercial models I can't share

Expected Behavior

Consistent behaviour no matter which API is used

Installed Versions

Details