Fix non-contiguous flow field and added EDT helper func

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 lines in your changes are missing coverage. Please review.

:exclamation: No coverage uploaded for pull request base (main@392d75a). Click here to learn what that means.

Files	Patch %	Lines
ultrack/imgproc/segmentation.py	88.88%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #79 +/- ## ======================================= Coverage ? 85.45% ======================================= Files ? 71 Lines ? 3911 Branches ? 0 ======================================= Hits ? 3342 Misses ? 569 Partials ? 0 ```

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