Simplify _cache_primal_status to use XPRS_SOLSTATUS

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 67.98%. Comparing base (96e1c6c) to head (81bad33).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #249 +/- ## ========================================== + Coverage 67.91% 67.98% +0.07% ========================================== Files 6 6 Lines 3341 3314 -27 ========================================== - Hits 2269 2253 -16 + Misses 1072 1061 -11 ```

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