Adds exception for restriced open-shell mean-field

[maxnus]

As title

[codecov[bot]]

Codecov Report

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

Comparison is base (511ef48) 71.53% compared to head (2d561a8) 71.53%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #151 +/- ## ======================================= Coverage 71.53% 71.53% ======================================= Files 152 152 Lines 20159 20161 +2 Branches 3343 3343 ======================================= + Hits 14420 14422 +2 Misses 4906 4906 Partials 833 833 ``` | [Files](https://app.codecov.io/gh/BoothGroup/Vayesta/pull/151?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BoothGroup) | Coverage Δ | | |---|---|---| | [vayesta/core/qemb/qemb.py](https://app.codecov.io/gh/BoothGroup/Vayesta/pull/151?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BoothGroup#diff-dmF5ZXN0YS9jb3JlL3FlbWIvcWVtYi5weQ==) | `73.89% <100.00%> (+0.05%)` | :arrow_up: |

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[basilib]

I've added an automatic conversion to UHF with a warning to deal with this.