Add async test method

[davegarred]

The current test framework can not be run under an async test. This adds an alternate method for processing a command that can be used instead.

[codecov[bot]]

Codecov Report

Merging #66 (86e1446) into main (814b602) will decrease coverage by 0.09%. The diff coverage is 81.55%.

@@            Coverage Diff             @@
##             main      #66      +/-   ##
==========================================
- Coverage   83.83%   83.75%   -0.09%     
==========================================
  Files          18       21       +3     
  Lines        2116     2117       +1     
==========================================
- Hits         1774     1773       -1     
- Misses        342      344       +2     

Impacted Files	Coverage Δ
src/lib.rs	100.00% <ø> (+44.44%)	:arrow_up:
src/test/mod.rs	29.41% <29.41%> (ø)
src/test/executor.rs	88.13% <88.13%> (ø)
src/doc.rs	57.03% <100.00%> (+0.10%)	:arrow_up:
src/test/framework.rs	100.00% <100.00%> (ø)
src/test/validator.rs	84.84% <100.00%> (ø)

... and 8 files with indirect coverage changes