Add .wast regression tests for fuse-{nez,eqz}

[Robbepop]

Carved out from #1512.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.36%. Comparing base (19abcfa) to head (2c962f8).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1569      +/-   ##
==========================================
+ Coverage   72.27%   72.36%   +0.09%     
==========================================
  Files         179      179              
  Lines       16330    16330              
==========================================
+ Hits        11802    11818      +16     
+ Misses       4528     4512      -16     

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