Expose async-trait to as a feature which can be enabled or disabled selectively

[slawlor]

Resolves #309

This is really a no-op change except assuring that all of the test coverage runs for both async-trait and no-async-trait usages.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.04%. Comparing base (f14e712) to head (70d06f8).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #313      +/-   ##
==========================================
- Coverage   82.19%   82.04%   -0.15%     
==========================================
  Files          61       61              
  Lines       11124    12182    +1058     
==========================================
+ Hits         9143     9995     +852     
- Misses       1981     2187     +206     

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