Fix memory_coloring pass when MIGRAPHX_NSTREAMS > 2

[kahmed10]

I noticed allocation segments reaching close to uint64 max value, which clearly would throw an out of memory error when trying to allocate on the GPU. This happened when MIGRAPHX_NSTREAMS was set to 2 or greater and the model somehow was large enough to trigger it.

Changing from auto to size_t seems to fix the issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.16%. Comparing base (6d02806) to head (2e23878).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3757   +/-   ##
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  Coverage    92.16%   92.16%           
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  Files          515      515           
  Lines        21978    21978           
========================================
  Hits         20256    20256           
  Misses        1722     1722           

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[TedThemistokleous]

I'd say pull this out of draft, I've confirmed this works across all the models we were testing this with.