Add NetCDF output functionality

[edejong-caltech]

• Adds helper code in the examples to output useful data from the box and rainshaft models as .nc files (used for importing data into PySDM for comparison)
• Also makes a small modification to the compute_standard_N_q function to make it type stable

[codecov[bot]]

Codecov Report

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

Project coverage is 97.63%. Comparing base (29b59bb) to head (3197f45). Report is 20 commits behind head on main.

:exclamation: Current head 3197f45 differs from pull request most recent head 71d2482

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #172 +/- ## ========================================== - Coverage 98.17% 97.63% -0.54% ========================================== Files 8 9 +1 Lines 493 508 +15 ========================================== + Hits 484 496 +12 - Misses 9 12 +3 ```

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