Refactor WasmInteger trait

[Robbepop]

Pulled out from #1512.

[codecov]

Codecov Report

Attention: Patch coverage is 72.41379% with 8 lines in your changes missing coverage. Please review.

Project coverage is 72.34%. Comparing base (88b0f41) to head (d1042df).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/core/src/untyped.rs	33.33%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1553      +/-   ##
==========================================
+ Coverage   72.32%   72.34%   +0.02%     
==========================================
  Files         179      179              
  Lines       16320    16328       +8     
==========================================
+ Hits        11803    11813      +10     
+ Misses       4517     4515       -2     

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[Robbepop]

Bug fixed in #1554. Ready to merge as soon as #1554 is merged.