Optimize Wasmi executor

[Robbepop]

This brings Wasmi main executor performance roughly on par with v0.36.2.

[codecov]

Codecov Report

Attention: Patch coverage is 70.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 81.34%. Comparing base (9f46524) to head (3387775).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/wasmi/src/engine/executor/instrs.rs	75.00%	2 Missing ⚠️
crates/wasmi/src/engine/executor/instrs/load.rs	66.66%	2 Missing ⚠️
crates/wasmi/src/engine/executor/instrs/store.rs	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1206      +/-   ##
==========================================
+ Coverage   80.80%   81.34%   +0.54%     
==========================================
  Files         299      302       +3     
  Lines       24886    24953      +67     
==========================================
+ Hits        20110    20299     +189     
+ Misses       4776     4654     -122     

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