move open_model from init to run

[eacharles]

Change Description

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New Feature Checklist

• [ ] I have added or updated the docstrings associated with my feature using the NumPy docstring format
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[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.05% :tada:

Comparison is base (ff3d6c1) 95.42% compared to head (0e5e981) 95.48%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #44 +/- ## ========================================== + Coverage 95.42% 95.48% +0.05% ========================================== Files 31 31 Lines 1596 1595 -1 ========================================== Hits 1523 1523 + Misses 73 72 -1 ``` | [Files Changed](https://app.codecov.io/gh/LSSTDESC/rail_base/pull/44?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC) | Coverage Δ | | |---|---|---| | [src/rail/estimation/estimator.py](https://app.codecov.io/gh/LSSTDESC/rail_base/pull/44?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC#diff-c3JjL3JhaWwvZXN0aW1hdGlvbi9lc3RpbWF0b3IucHk=) | `100.00% <100.00%> (ø)` | | | [src/rail/estimation/summarizer.py](https://app.codecov.io/gh/LSSTDESC/rail_base/pull/44?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LSSTDESC#diff-c3JjL3JhaWwvZXN0aW1hdGlvbi9zdW1tYXJpemVyLnB5) | `60.00% <100.00%> (+1.07%)` | :arrow_up: |

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