Add a helper function to retrieve N_liq, N_rai, q_liq, q_rai

[edejong-caltech]

Purpose

To-do

Content

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• [ ] I have read and checked the items on the review checklist.

[codecov[bot]]

Codecov Report

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

Project coverage is 98.06%. Comparing base (bdac538) to head (a4f2733).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #143 +/- ## ========================================== + Coverage 98.00% 98.06% +0.05% ========================================== Files 8 8 Lines 452 465 +13 ========================================== + Hits 443 456 +13 Misses 9 9 ```

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