remove uint64 and int64

[StRigaud]

Metal as an incompatibility with 64-bits int, for simplicity we remove support for uint64 and int64.
closes #286

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.76%. Comparing base (414f193) to head (58b7775).

❗ Current head 58b7775 differs from pull request most recent head 561f305. Consider uploading reports for the commit 561f305 to get more accurate results

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #296      +/-   ##
==========================================
+ Coverage   55.61%   55.76%   +0.15%     
==========================================
  Files         232      232              
  Lines        3704     3694      -10     
  Branches     1472     1470       -2     
==========================================
  Hits         2060     2060              
+ Misses        493      483      -10     
  Partials     1151     1151              

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