refactor(kernels::grisubal): improve dart preallocation code

[imrn99]

replace a quadratic loop with a proper scan at two occurences

[codecov-commenter]

Codecov Report

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

Project coverage is 82.62%. Comparing base (308afbb) to head (290094a).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #211 +/- ## ========================================== + Coverage 82.60% 82.62% +0.01% ========================================== Files 41 41 Lines 5865 5870 +5 ========================================== + Hits 4845 4850 +5 Misses 1020 1020 ```

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