algorithm,memory,numeric: Improve thrust compatibility via ADL barriers

[stotko]

The recently introduced custom pair implementation in #425 resulted in regressions when using thrust's algorithms that have also been implemented by us, e.g. thrust::copy(...). This is caused by ADL since pair now is a member of the stdgpu namespace rather than thrust as before. Use ADL barriers to ensure that calling any algorithm from thrust will not accidentally delegate to our implementation.

Fixes #432

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.34%. Comparing base (3333da6) to head (84386f6).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #433      +/-   ##
==========================================
- Coverage   97.38%   97.34%   -0.04%     
==========================================
  Files          32       32              
  Lines        2524     2524              
==========================================
- Hits         2458     2457       -1     
- Misses         66       67       +1     

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