Fix incorrect weighting used for permafrost pool adjustment

[bpbond]

The simpleNbox::stashCvalues function was using incorrect biome weights when adjusting the permafrost pools. This resulted in extremely bad behavior when using more than a single biome.

This initial PR is a straight bug fix, and should not change main behavior at all (because permafrost remains disabled). I'll open a second PR to evaluate the effects of turning on permafrost by default in v3.

Part of #675

[github-actions[bot]]

Differences in Hector outputs

Hello, this is leeyabot!

The current pull request's outputs do not differ from 3.0.0 (9aebf67).

[codecov-commenter]

Codecov Report

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

Comparison is base (0ea644b) 79.72% compared to head (3df6b20) 79.72%.

:exclamation: Current head 3df6b20 differs from pull request most recent head f86983b. Consider uploading reports for the commit f86983b to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #720 +/- ## ======================================= Coverage 79.72% 79.72% ======================================= Files 61 61 Lines 5978 5978 ======================================= Hits 4766 4766 Misses 1212 1212 ```

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[github-actions[bot]]

Differences in Hector outputs

Hello, this is leeyabot!

The current pull request's outputs do not differ from 3.0.0 (9aebf67).