small cleanup of the OCFL track filling in function

[WPringle]

moving carq_ref to above holland B calculation and just using that to compute it instead of needing to take the nanmean

[codecov[bot]]

Codecov Report

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

Project coverage is 91.74%. Comparing base (9ebe0bc) to head (d5c53bf).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #109 +/- ## ========================================== - Coverage 91.74% 91.74% -0.01% ========================================== Files 19 19 Lines 2012 2010 -2 ========================================== - Hits 1846 1844 -2 Misses 166 166 ```

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