Cast to uint64 when relabeling segmentations in sample data

[cmalinmayor]

Proposed Change

Fixes a problem when I added sample data with more segmentations that the labels wrapped. (I didn't actually add the sample data in this PR)

Checklist

Go through these things before merge. Actions should run automatically to test them, but for information on how to run locally, see CONTRIBUTING.md.

• I have added tests that prove that my feature works in various situations or tests the bugfix (if applicable).
• I have checked that the tests pass and I maintained or improved test coverage (if applicable).
• I have written docstrings and checked that they render correctly in the documentation build.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.41%. Comparing base (4614349) to head (ef5c681).

Additional details and impacted files

@@              Coverage Diff              @@
##           v0.2.1-patch      #40   +/-   ##
=============================================
  Coverage         89.41%   89.41%           
=============================================
  Files               650      650           
  Lines             60090    60091    +1     
=============================================
+ Hits              53731    53732    +1     
  Misses             6359     6359           

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