exclude demo, benchmarks and profile from coverage

[ahoy196]

In the course of #507 @milessabin proposed that we exclude demo, benchmarks and profile from coverage for straightforward reasons.

@armanbilge proposed a mechanism of doing so, which is the path followed in the current PR which addresses the same. This uses the coverageEnabled flag in sbt project settings.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7c78389) 67.10% compared to head (590e9fa) 72.37%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #508      +/-   ##
==========================================
+ Coverage   67.10%   72.37%   +5.26%     
==========================================
  Files          40       32       -8     
  Lines        4682     4340     -342     
  Branches      951      927      -24     
==========================================
- Hits         3142     3141       -1     
+ Misses       1540     1199     -341     

see 9 files with indirect coverage changes

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[ahoy196]

I went ahead and excluded docs and unidocs as well from the coverage.

[milessabin]

LGTM!