DST fault injection bug fix

[vaibhawvipul]

• handle aio errors
• add assertions (fixes - issue 266)

[guergabo]

fyi: we had pair programming session this morning and few additional things were discovered / discussed. In particular the handling of failure injection post-process. Since the model will encounter reads that it was not aware of since the client believed the AIOStoreFailure occurred. Good stuff!

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 28 lines in your changes are missing coverage. Please review.

Project coverage is 63.70%. Comparing base (2ff886c) to head (681718b).
Report is 1 commits behind head on main.

Files	Patch %	Lines
test/dst/model.go	15.15%	20 Missing and 8 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #267      +/-   ##
==========================================
+ Coverage   62.27%   63.70%   +1.43%     
==========================================
  Files         113      113              
  Lines        9706     9717      +11     
==========================================
+ Hits         6044     6190     +146     
+ Misses       3169     3070      -99     
+ Partials      493      457      -36     

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