[AlgorithmSelection] Rename BackendSelection, introduce Backend type

[mtfishman]

No description provided.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.32%. Comparing base (ceb26a7) to head (8a70717).
Report is 11 commits behind head on main.

❗ Current head 8a70717 differs from pull request most recent head 51d64f3. Consider uploading reports for the commit 51d64f3 to get more accurate results

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Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1407       +/-   ##
===========================================
+ Coverage   49.23%   85.32%   +36.09%     
===========================================
  Files         110      127       +17     
  Lines        8320     9031      +711     
===========================================
+ Hits         4096     7706     +3610     
+ Misses       4224     1325     -2899     

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